Originally Posted by
Transmutable
It has to do with how the color is being made, additive (light) or subtractive (pigment). The primary colors of LIGHT are red, blue, and green, which is why web colors are given in RGB code. So #005599 uses no red, 33 units (I forget how it's measured) of green, and 99 units of blue to create that light, slightly greenish blue. The primary colors of PIGMENT are red, yellow, and blue, which is why restaurants give out those three crayons to make kids reasonably happy with their color dining experience. Combining the three primary colors of light gives you white, and combining the primary colors of pigment gives you black or brown.