My first (and so far, only) wife recently gave me a gift: a black scarf that she had crocheted. The scarf wasn't all black — positioned at appropriate positions were colored yarn so that the scarf mimicked the visible emission spectrum of hydrogen! (OK, so both my wife and I are geeks . . . .) She said that she let each row stand for 1 nmr of wavelength so that the scarf represented the 300-nm range that is commonly used to define the approximate limits of visible light. I now look forward to the cold weather so I can wear it. I wondered what inspiration a Balmer-series scarf might provide me for a column for "The Baseline." Once again, my wife gave me a gift — an idea. Why not a column on color?
A discussion of the history of the discovery of color is best found elsewhere. However, probably the single largest advance in the understanding of color was when Isaac Newton demonstrated in the early 1670s that white light was a combination of all colors of light. This makes color perception an issue of variable absorption (or, equivalently, variable reflection) of different components of white light. Objects do not emit color; rather, they absorb and reflect colors in different amounts, allowing them to be perceived as colored based upon what colors they do and do not absorb.Spectral Colors
Spectral colors are also called monochromatic and are sometimes referred to as pure colors. The colors are commonly separated into six or seven main regions: red, orange, yellow, green, blue, and violet (the familiar ROY G. BV). Some people add indigo as a separate color, making ROY's last name BIV. However, there is still debate as to whether indigo deserves to be a separate color. It should be noted, though, that the identification of these six (or seven) specific colors as "the" colors of the rainbow is completely arbitrary! However, they are so ingrained in our society that they seem to be the "natural" colors.
As mentioned earlier, objects have a color caused by what colors of light are reflected from them. However, objects may not have a spectral color, because more than one wavelength (or more correctly, range of wavelengths) can be reflected simultaneously. Also, the relative amount of light reflected will influence the apparent color of the object. An object that reflects both blue and red may look bright pink or burgundy, depending upon the relative amounts of red and blue light that are reflected. Note that neither "bright pink" nor "burgundy" is in our list of spectral colors. The spectral colors may themselves be complete as a set, but their number of possible combinations is literally infinite.
Representing Colors With Light
In addition to the absorption–reflection process, different colors can be generated another way: as the emission of lights of certain colors. These colors are referred to as additive colors. Different combinations of colored lights of various intensities will yield different perceived colors. Again, we cannot have an infinite number of differently colored lights, each one representing a different spectral color. Instead, we rely upon various standard combinations that can be varied to generate an overall light color of different types.
An RGB color model is probably most visible if you take a very close look at your television or computer monitor: the entire screen is full of tiny red, green, and blue dots called pixels. The intensity of each pixel color is varied to produce the desired color. Because of different manufacturing processes and materials, however, a color image may look different from one output device to another, leading to some variation in perception of color in many consumer products. Thus, there is no single "RGB" color model; several specific RGB color models have been defined industrially, by Microsoft and Adobe for example. Specifying an exact color also requires that you define which system, or color space, you are using.
The RGB color model might make biological sense, but it is not the only possible model. Any set of colors — usually but not required to be three — that can stimulate the three different cones in the retina can be used to generate colored light.