Introduction
Color is the byproduct of the spectrum of light, as it is reflected or absorbed, as received by the human eye and processed by the human brain. It's also a great design element!
Here's a surface level overview of how it all works:
The world is full of light. Visible light is made of seven wavelength groups. These are the colors you see in a rainbow: red, orange, yellow, green, blue, indigo, and viole, the Mr. ROY G. BIV you might have been introduced to in elementary school science. The reddish colors are the long wavelengths. The greenish colors are the mid-size wavelengths. The bluish color are the short wavelengths.
When light hits objects, some of the wavelengths are absorbed and some are reflected, depending on the materials in the object. The reflected wavelengths are what we perceive as the object's color.
Our eyes are the input channels, if you will, for this light. One portion of the eye is called the retina and it contains four types of light sensors. First are the rods, which record brightness and darkness and from which we "see" a sort of coarse sketch of the world. Next are three types of cones, each one optimized to absorb a different spectrum range of visible light. One set of cones absorbs long wavelengths, the reds. Another absorbs mid-size wavelengths, the greens. The third absorbs short wavelengths, the blues. Together, these rods and cones gather the information that our brain then processes into one combined image.
Additive and Subtractive Color
The tools we use to describe color are different when the color is printed than from when it is projected. Projected color is additive. Printed color is subtractive.
Visible light is a small part of the electromagnetic spectrum, between the wavelengths of 400 and 700 nm (nanometers = billionth of a meter). In 1666 Sir Isaac Newton used a glass prism to refract white light at different angles according to wave length. He saw a rainbow of colors, which he passed through a second prism to re-form white light. He concluded that white light is a mixture of all the colors of the visible spectrum.
Sir Newton was playing with additive color. No light (or color) is black. All light (all colors) is white.
Each color of the spectrum has a specific frequency. Adding different colors of light together increases the number of frequencies present and the more colors you add the closer it becomes to white. Therefore, light is called an additive color mixing system. This type of color mixing is used in computer monitors, TV sets, and to illuminate actors on stage.
Subtractive Color
The color we see on paper is created using a subtractive model, where the frequencies that are not absorbed form the color we see.
When you project light, you are sending out frequencies of light that add together to form a certain color beam. Think of it as painting with light. In contrast, the color we put down on paper works exactly the opposite. The color we we see is the spectrum of light which is reflected by the paper or by the ink, crayon, or marker we put on the paper.
Historically artists and designers have not worked with light but with paints and pigments. Colors of paint absorb most of the light frequencies and reflect back only the wavelength that defines the color you see. Mixing different paints makes a darker color because more of the light frequencies are absorbed. This method of mixing colors is called subtractive because each color absorbs, light frequencies, subtracting them from the total mixture.
A subtractive color model is the very first type of color we learn as a child, when we are taught that the three primary colors of red, yellow, and blue can be mixed to form all colors. The printing inks magenta, yellow, and cyan are essentially a more sophisticated version of our childhood crayons.
Color Gamut
The gamut is the set of possible colors within a color system. No one system can reproduce all possible colors in the spectrum.
Unfortunately for designers, it is not possible to create every color in the spectrum with either additive or subtractive colors. Both systems can reproduce a subset of all visible color, and while those subsets generally overlap, there are colors which can be reproduced with additive color and not with subtractive color and vise-versa.
The colors that can be created by each system are called a "gamut". The ACM diagram to the left, shows the relative gamuts of additive (monitor display) and subtractive (printed) color. The larger area on the graph represents all visible color.
Describing Color
There are lots of different ways to describe color. These are some of the most common terms you'll hear. Click on any one to learn more.
Color Terms
Hue The name we give to a distinct part of the spectrum "red" "yellow" "purple"
Saturation The "purity" of a color, how much Grey is or isn't in it.
Value (or Intensity or Lightness) The "brightness" or "darkness" of a color, the amount of a brightness, light, or white in the color.
Primary The three defining colors of a color wheel, from which all other colors are built.
Secondary The three colors created by blending two primary colors.
Tertiary The six colors created from the three primary and three secondary colors.
Complementary Colors at opposite sides of the color wheel, high contrast with each other.
Triad Set of three colors equidistant around the color wheel.
Analogous Colors next to each other on the color wheel.
RGB Red, Green, Blue. The primary colors in the additive model.
CMYK Cyan, Magenta, Yellow, Black. The primary colors in the printer's version of the subtractive model. Black is added to the mix for sharpness of the printed image.
RGB Color
RGB stands for red, green, blue, the three colors that make up an image on a monitor.
The RGB color model is an additive model used for displaying images on a computer monitor or other screen device. When the three primary colors, red, green, and blue, are combined they make a white light. When all are absent, there is black. Projected colors often feel much brighter than their subtractive model counterparts.
To create RGB colors on the computer you must specify percentages of each of the primary colors. Color is controlled by moving the sliders:
This purple color is a mix of 56% red, 5% green, 61% blue: 
CMYK
CMYK stands for cyan, magenta, yellow, black -- the four colors that make up the standard printing process.
The CMYK color model is a subtractive model used for printing on printing presses and many color computer printers. When the three primary colors, cyan, magenta, and yellow, are combined together they do not produce a rich black, so black ink is added as a fourth color.
To create CMYK colors on the computer you must specify percentages of the primary colors. Color is controlled by moving the sliders.:
For example, this purple color is a mix of 5% cyan, 56% magenta, 0% yellow, and 39% black:
Process printing is the printing of images on paper using overlapping dots of cyan, magenta, yellow, and black (CMYK) inks to create full color, continuous tones. If you look at a printed photo with a loupe, you'll see it is really made of many small dots of these four colors. Many color computer printers, especially those designed to print photographs, use CMYK inks also
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| Original full color photograph. | Enlarged representation of CMYK inks printed in a dot structure (halftone) to create the illusion of full color imagery. |
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Enlarged representation of CMYK inks printed in a dot structure (above). To the right, is each color broken out individually: cyan at the top, followed by magenta, yellow, and black. |
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