What are the properties of Red/Green/Blue that make them the primary colors for light? Are they the only set of three colors that could combine to make all other colors?

Question

And I have the same question for pigment primary colors (magenta/cyan/yellow).

In: Physics

Answer 1

Wrong, wrong, wrong. The three cones detect: blue, green, and yellow-green. The last one detects red at the edge of its sensitivity. That is why there are so many wavelengths seen as blue-green (because they stimulate all three cones) and why red seems to fade from combinations of pigments (because it is detected at low sensitivity).

People who have had a crystalline lens removed can see ultraviolet light. The lens normally filters it out, but the blue cone reacts to it.

Carmine is one color that cannot be expressed as an RGB value. It requires a “super” Red to make it from a mixture of primary colors. There are others that require a “super” Blue. The “tongue” or CIE diagram shows this by going outside the ordinary maximum lines.

So, RGB is an approximation for computer screens; CYMK for printing. Neither is good enough to describe all colors that normal humans can see.