Way back in 2005, rutt posted the best summation of how colors work as light I’ve ever seen, at DigitalGrin.com.

Rather than force you over there to read that post, I am replicating it right here, as it required a few edits for clarity.

“In order to understand the relationship of LAB, RGB, and CMYK, we have to understand that the colors are actually defined in terms of one another.

1. Red is a primary in light.
2. Cyan is the pigment opponent of red. It is defined as the pigment that reflects green and blue perfectly but no red at all. So in light, cyan is composed of equal parts green and blue, but no red.
3. Green is a primary in light.
4. Magenta is the pigment opponent of green. It is defined as the pigment that reflects red and blue equally, but no green at all. So in light, magenta is composed of equal parts red and blue, but no green at all.
5. Blue is a primary in light.
6. Yellow is the pigment opponent of blue. It is defined as the pigment that reflects red and green equally, but no blue at all. So in light, yellow is composed of equal parts red and green, but no blue at all.

Given these definitions, we can see why the pairs green, magenta and blue, yellow are called opponents. There can be no green at all where there is magenta, by definition. Shine a green light on a magenta surface and you see black; nothing is reflected. Magenta is defined in terms of what it doesn’t have, namely green. Continue Reading