HOW COLOR WORKS

Color is actually a function of the eye. It sorts wavelengths of light and makes them visible as different colors. Mixtures of wavelengths make lighter colors.

Here is a list of frequently asked questions:

eye parts How does the eye work?

The eye is like a camera. It has the following parts:


retina parts How does the retina work?

The retina is like the light sensitive part of a digital camera:


Are the eyes of other animals the same as human eyes?

Different animals have different visual systems:


The following information applies mainly to human vision:


eye spectral response How does the retina respond to different colors of light?

The spectral response of this color system is shown at right.

The main colors of spectral light (with wavelength and frequency) are:

  WavelengthFrequency ColorRed ConeGreen ConeBlue Cone
  400 nm750 THz violethalfnonehigh
  460 nm650 THz bluenonenonehigh
  520 nm610 THz cyannonehighhigh
  520 nm580 THz greennonehighnone
  570 nm530 THz yellowhighhighnone
  590 nm510 THz orangehighhalfnone
  670 nm450 THz redhighnonenone

Nonspectral colors are also produced:

   ColorRed ConeGreen ConeBlue Cone
   whitehighhighhigh
   grayhalfhalfhalf
   blacknonenonenone
   magentahighnonehigh
   pinkhighhalfhalf
   brownhalflownone
   olivelowhalfnone

Every color appears on this color map or on a darker version of it. A larger version is below.

color map

analog encoder How does the retina encode color?

The retina uses an analog matrix to encode color detected by the cone cells:

These matrix encoders are placed over most of the surface of the retina so different objects appear different colors.

COLOR MATRIX OUTPUTS

 yelmid +blu 
grn       grn
+       +
mid       mid
       
red       red
 yelmid +blu 

How the brain interprets the matrix:

  • The horizontal axis of the table shows the output of the blue-yellow bipolar cell for the color being looked at.
  • The vertical axis of the table shows the output of the green-red bipolar cell for the color being looked at.
  • The output of the brightness bipolar cell for the color being looked at determines how dark the color is.
  • The brightness is not shown in the table at left. Its axis would be perpendicular to the screen.
  • Any color can be described as the three outputs of the matrix: brightness, blue-yellow, and green-red.
  • The color matrix assures that the same color seen under many conditions appears to be nearly the same.
  • The outer periphery of vision is usually black and white and out of focus. It notices movement.
  • Psychological primaries are 4 points where one differential output is centered while the other is at an extreme.
  • Psychological primaries have no use other than psychological effects. Colors cannot be mixed with them.
  • Other primaries are used to mix colors.
  • The NTSC US color TV system (1953-2007) used the corners of the eye matrix to hide signal errors.
PSYCHOLOGICAL
PRIMARIES
  Cerise
  Yellow
  Aqua
  Blue
separator
NTSC COLOR TV
PRIMARIES
  Vermillion
  Lime
  Sky
  Purple

eye spectral response Why can't I see color at night?

The retina contains three different kinds of light sensitive cells that work in daylight, but only one kind of cell that works at night:


primary colors What are primary colors?

Primary colors are sets of colors that can be used to mix all of the other colors.

The primary colors depend on the kinds of color preceptors present.

Then number of primary colors depends on the number of types of color preceptors.

Why are there three primary colors?

There are three primary colors because there are three kinds of color vision cones in the human retina.

Primary colors are chosen to differentially activate the three kinds of cones to mix many different colors.

The better the choice of primary colors, the larger is the gamut of colors that can be mixed with them.

Do animals have primary colors?

If they have color vision, they have primary colors.

Since animals do not try to mix colors, they don't know or need to know about primary colors.


Why are there several different sets of primary colors?

The primary colors in these different sets are used for different purposes:

The primaries of light are used for mixing colored lights.

The light primaries are
   RED,
   GREEN, &
   BLUE.

primary colors of light These are the colors where each retinal pigment is most isolated from responses of the other two pigments. Varying these primaries gives the largest possible gamut of colors from using three primaries.

These primaries are used for producing light sources, stage lighting, color photography, color television, separated dots of pigment, and mixing colors on rotating discs.

These are additive primaries because they work toward white when mixed.

The primaries of pigments are used for mixing transparent paints and dyes.

The pigment primaries are
   MAGENTA,
   YELLOW, &
   CYAN.

primary colors of pigment These are the colors where each pigment removes the most of one of the light primaries without removing much of the other two primaries. Varying these primaries gives the largest possible gamut of colors from using three primaries.

These primaries are used for transparent dyes, water colors, color printing, photographic prints, paint mixing, and photography color filters.

These are subtractive primaries because they work toward black when mixed.

The primaries of oils are used for mixing oil paints.

The oil primaries are
   RED,
   YELLOW, &
   BLUE.

primary colors of oil paint/old primaries These colors work for oil paints, because they have unique properties that other color media do not have. They do not work with other kinds of color mixing.

These are part additive and part subtractive because they behave differently at different concentrations.

Quattron primaries for TV sets.

The Sharp Quattron TV primaries are
   RED,
   YELLOW,
   KELLY, &
   BLUE.

primary colors of light This is an attempt to increase the gamut of colors a standard color display can make.

What it does is allow the green to make a better cyan by taking the job of making yellow away.

Since it uses a standard TV signal, it just adjusts the colors produced.

AutoVary primaries for TV sets.

The Autovary primaries are
   RED,
   LEAF,
   KELLY, &
   BLUE.

primary colors of light This is an attempt to increase the gamut of colors a standard color display can make.

What it does is allow the green to make a better cyan by shifting it between leaf and kelly depending on the decoding angle of the color signal.

Since it uses a standard TV signal, it just adjusts the colors produced.

Psychological primaries can't mix colors.

The psychological primaries are
   CERISE,
   YELLOW,
   AQUA, &
   BLUE.

color wheel These are used only for human vision experiments. They have no value for mixing colors.

Notice that these colors are at right angles to each other on the color wheel (below).


What is the color map?

large color map The color map is a map of the gamut of all possible colors the eye can see.

Note the colors on this screen are approximate.

What are the spaces outside the curve?

These are colors the eye cannot see because they would require stimulating the cone cells individually rather than all at the same time.

What are the numbers around the edge of the map?

They are the wavelengths in nanometers of the colors at those points.

Why are there no wavelength values along the bottom edge?

The colors there are nonspectral colors. They are mixtures of sets of spectral colors, as are all of the colors in the interior of the map.

What are the numbers along the x axis?

The x axis is the portion of the total stimulation received by the eye that is red.

What are the numbers along the y axis?

The y axis is the portion of the total stimulation received by the eye that is green.

Where are the numbers for blue stimulation?

The z axis is perpendicular to the page. On the top surface of the map, the values are x + y + z = 1.

What about darker colors?

These are on layers under the map visible here where x + y + z = t and t is a value between 0 and 1. See below.

What is the curved line across the center of the map?

This is the line of colors produced by black body radiation. The numbers are the black body temperatures in Kelvins.

What is the point marked E on the map?

This is the equal energy point where red, green, and blue are equal at 5500 K.
x = 1/3, y = 1/3, and z = 1/3.

What is the triangle containing segments A and D?

This is the gamut of colors displayed on a color TV or monitor. All colors outside this triangle are displayed wrongly on this screen.

What is the white triangle?

This is the gamut of colors visible under a white LED lamp.

What is the quadrilateral containing segments B and D?

This is the gamut of colors displayed on an Autovary color TV or monitor.

What is the quadrilateral containing segments C and D?

This is the gamut of colors displayed on a Quattron color TV or monitor.


isometric color map What is the isometric color map?

The isometric color map is the map of the gamut of all possible colors the eye can see.

The isometric color map is shown so that all three axes are visible.

This is the same map as above, but shown over the isometric view point instead of over the Z axis.

Again, only the top layer where x + y + z = 1 is visible.

What is the triangle around the map?

This is the limit of the area where x, y, and z are all simultaneously nonnegative.

What are the other features of the isometric color map?

The spaces outside the colored space are colors the eye cannot see.
 - This is because they would require stimulating cone cells individually rather than collectively.

Numbers around the curved map edge are wavelengths in nanometers of colors at those points.

Colors along the straight edge of the map and in the map interior are nonspectral colors.
 - They are mixtures of sets of spectral colors.

Numbers along the diagonals are portions of the total cone stimulation projected from x and y axes.

Darker colors are on layers under the visible map where x + y + z = t and t is between 0 and 1. See below.

What is the curved line across the center of the map?

This is the line of colors produced by black body radiation.
 - The numbers are the black body temperatures in Kelvins.

Notice that the equal energy point E where red, green, and blue are equal is at 5500 K.
 - In this view, it is closest to being over the origin of the graph.

Why is the red end of the spectrum not at a corner?

Both the red and the green cone are stimulated at the red end of the spectrum.

Why is the blue end of the spectrum not at a corner?

Both the blue and the red cone are stimulated at the blue end of the spectrum.

Why is the green part of the spectrum not at a corner?

The green cone is never stimulated alone. Red and blue cones are stimulated at all green wavelengths.

Why are multiple cones stimulated at the ends of the visible spectrum?

The ends of the spectrum are the limits where the cornea and lens stop passing light.

What does it mean where the colored area touches the triangle?

It means that one cone is receiving very little stimulation.
 - This happens on a line between red and yellow, at aqua, and at violet.


3-D color map iso 3-D color map

What is the 3-D color map?

The 3-D color map shows the darker layers underneath the usual map.

The diagram shows the full strength, 2/3, 1/3, and 1/12 bright colors.

There are infinite layers between black at the bottom and the regular map.

The closer a layer is to the bottom, the darker the colors are.

The leftmost diagram shows how the layers infinitely stack together.

Black is at {0,0,0} at the lower left corner.

Red (x) cone alone is at {1,0,0} at the lower right corner.

Green (y) is at {0,1,0} at the top corner.

Blue (z) is at {0,0,1} at the lower front corner.

Every possible visible color is present in this map.


What is the old color wheel?

The old color wheel is based on using the oil paint primaries as the basis of color.

The oil primaries are:
 
   RED
   YELLOW
   BLUE

old color wheel What is wrong with using the old color wheel?

It does not cover the entire gamut of visible hues. Colors are subdued.

It works for only oil colors.

It does not contain all of the scientific primaries.

What is the new color wheel?

The new color wheel is based on the scientific primaries of light and of pigment.

The light primaries are:
 
   RED
   GREEN
   BLUE

The pigment primaries are
 
   MAGENTA
   YELLOW
   CYAN

new color wheel What is right with using the new color wheel?

It covers the entire gamut of visible hues. Colors are vivid.

It works for all color mixing except oil paint.

It does contain all of the scientific primaries.

Complementary colors are actually on opposite sides of the wheel.


Why is there a color wheel when the spectrum is a straight line?

Notice the following:

  • The red cone has a secondary peak at violet.
  • Color map violet has a positive x (red response).
  • The green-red bipolar cell thus sees violet as red.
  • Thus, violet is on the red side of the color matrix.
  • The color matrix has a range for violet thru cerise.
  • The color matrix has colors encircling white.
  • The eye sees magenta as red and blue mixed.
  • Cerise, magenta, and purple fill the matrix gap.
LIMGRN AQUCYN SKY
LEF+LIM +AQU+SKY AZU
YEL+YEL WHT+BLU BLU
ORN+VER +CER+PUR VIO
VERRED CERMAG PUR
eyespectrum color map new color wheel

How is an equally spaced color wheel made from the color matrix?

Like this:

 GRN AQUCYN  
LEF     AZU
YEL  WHT  BLU
ORN     VIO
 RED CERMAG  

With these
equally
spaced
primary
colors:

 GRN  CYN  
       
YEL  WHT  BLU
       
 RED  MAG  

Rounding
off of
the first
diagram:

new color wheel from matrix

Which is
just a
rotation
of the new
color wheel
diagram
used on
this site:

new color wheel

How are colors mixed?

What is additive color mixing?

Additive color mixing combines colored light together.

The additive color mixing result is lighter.

Additive color mixing uses the primary colors of light.

All primaries in equal amounts mix to make white.

Complementary colors mix to make white.

primary colors of light

        +    =   

        +    =   

        +    =   

   +    +    =   

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    + =

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+ + =

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    + =

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    + =

+ + =

What is subtractive color mixing?

Subtractive color mixing combines colored filters together.

The subtractive color mixing result is darker.

Subtractive color mixing uses primary colors of pigments.

All primaries in equal amounts mix to make black.

Complementary colors mix to make black.

primary colors of pigment

        +    =   

        +    =   

        +    =   

   +    +    =   

+ =

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    + =

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+ + =

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    + =

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    + =

+ + =


new color wheel What are complementary colors?

Complementary colors are colors that mix additively to produce white.


What happens if the wrong primaries are used?

Used For Light Used For Pigments Used With Oil Paint
Old
Primaries
Light
Primaries
Pigment
Primaries
Old
Primaries
Light
Primaries
Pigment
Primaries
Old
Primaries
Light
Primaries
Pigment
Primaries
old primaries light light primaries pigment primaries light Old primaries pigment Light primaries pigmemnt Pigment primaries Old primaries oil Color Matrix Encoder Pigment primaries oil
  1. If the wrong primaries are used, the wrong colors appear.
  2. Using the wrong primaries gives a smaller gamut of colors.
  3. Notice the complete lack of greens with the old primaries.
  4. Colors are pastel with the wrong primaries for light.
  5. Colors are dark with the wrong primaries for pigment.
  6. The color-sensitive cones in the eye dictate the primary colors.
  7. Oil paints use partly light mixing and partly pigment mixing.
  8. The color-sensitive cones in the eye dictate the primary colors.

See Teach the correct primary colors for more about this.


Do some people have eyes different from the eyes of most people?

visual defect color wheel Yes. There are several genetic differences in the eyes of some people.

The color wheel at right shows some of the defects (outside ring is normal).

The following are forms of color vision defects:

- Notice that protan and deutan defects make the green-red bipolar cells quit or malfunction.

- Notice that tritan defects make the blue-yellow bipolar cells quit or malfunction.

The following are forms of undocumented color vision supposedly found only in human women:

This is covered in more detail at Human Color Vision Defects.


Can some people with defective color vision do something about it to see more normally?

Yes. There are several tricks to see more colors:

This is covered in more detail at Human Color Vision Defects.

Links: