Name: Ryan M.
As both an aspiring artist and scientist, I have always
been perplexed by the contradiction between the two as far as primary
colours are concerned.In science the primary colours are red, green and
blue. This makes sense as it can be proved with a ray box. However, in
art the primary colours are said to be blue, red and yellow and red
which is believable as with these colours all other colours can be
The theory of color is NOT straightforward. It involves chemistry, physics,
physiology, and psychology.
In fact it is possible to create color from "black and white" transparencies
exposed using different filters!!
And the now common place digital cameras produce colors from electronic
pixels that have no intrinsic color at all. What is a poor artist to do?? I
have just finished reading the best presentation of this complicated subject
from an artist's perspective, which you will find very readable and
fascinating. The book is titled:
"Bright Earth: Art and the Invention of Color" by Philip Ball [ISBN
0-226-03628-6] The University of Chicago Press. Fascinating reading for
scientist and artist alike.
The first thing to realize is that the number of "primary" colors depends
on the type of creature that is doing the looking. Normal cones in the
human eye sense light in broad color bands in the red, green and blue-violet
regions of the spectrum. These bands overlap a great deal.
Thus, for humans, mixing various amounts of three colors of light (red,
green and blue) will produce all colors that can be perceived. That is for
an additive source like a computer monitor or TV screen that produces
The human eye is sensitive to broad bands of light wavelengths, and thus the
eye is not a spectrometer: it interpolates colors depending which of the
three cones are receiving light. For example, there are two ways to make
"yellow" light. 1) use equal amounts of red and green light. These
stimulate the red and green cones, and the brain sees "yellow". 2) use a
wavelength of light that is between red and green (about 565nm). Because
the response of the red and green cones overlaps, this single color also
stimulates both the red and green cones. The brain sees "yellow in both
There are three types of color blindness, depending on which color sensor is
For pictures using paint or ink, it gets a little more complicated because
what happens to the light before it strikes the eye is a two-step process.
Inks are subtractive. They block various colors of light and only the
colors that are NOT blocked are reflected from the paper to your eyes.
For example, yellow ink absorbs blue light, but allows red and green light
to reflect from the paper. The human eye sees yellow which is red and
green. Cyan, which is a sort of green/blue, absorbs red, but lets blue and
green light reflect from the paper. So if you put both yellow and cyan ink
on the paper, only green light gets through to the eye. Similarly, magenta
is a purplish-red color that absorbs green.
Dogs seem to have only two kinds of color receptors in the eye. They see
fewer separate colors. Many birds have four or more types of cones (the
extra one is ultraviolet). They see potentially many more colors than
humans, depending on how the brain perceives this color. Birds would need a
TV with four primary colors, or paper with four different kinds of inks for
their full color vision.
More information can be found in encyclopedias.
The easiest thing to do is point you to the following web site which I
believe does a good job describing the differences between
Red-Green-Blue, Red-Blue-Yellow, and Cyan-Magenta-Yellow and what is
meant by Primary Colors.
The colors of paint and crayons do not add color to the light we see; they
absorb light from it. A "perfect" set of paint colors is in fact magenta,
yellow, and cyan. For most human eyes, magenta is very close to red and
cyan is very close to blue. Yellow is yellow. Red, yellow, and blue will
work almost as well as magenta, yellow, and cyan. Also, red, yellow, and
blue are all well known colors, easier to talk about.
Magenta paint will remove green from white light, reflecting back red and
blue. Yellow removes blue light, reflecting back red and green. Cyan
absorbs red, reflecting green and blue. If you combine cyan and yellow
paint, red and blue are absorbed. In white light, this reflects only green.
This is why blending blue and yellow paint gives you green.
Math, Science, Engineering
Illinois Central College
The spectral primaries are pure colors and deal with light sources. The
light impinging on an object is, for example, red. No matter what "color"
the object might appear when illuminated with white light it will appear
red when the light source is pure red (assuming at least some of the light
is reflected instead of absorbed).
In are you very rarely have light of a pure color. Instead, an object
appears red because it absorbs all colors except red. The red light is
reflected to our eyes.
This difference is why when you mix red, green, and blue light sources you
perceive white light but if you mix red green and blue colors you get
black. The red color absorbs green and blue, green absorbs red and blue
and blue absorbs red and green. The net result is all colors of light get
absorbed and you perceive black.
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Update: June 2012