Why does blue and yellow make green?

Question

When the three primary light colors are red, blue, and green. It seems odd that the three primary paint colors are red, blue, and yellow. Why does the yellow replace green as a primary color?

Answer 1

Good question.

The human eye contains three types of cone cells.  Each type is most sensitive to a certain frequency.  The three key frequencies are roughly red, green, and blue.  If all three cone cells are stimulated equally, we perceive the sensation as "white".  If the blue-type cone cells are stimulated, but the red and green ones aren't, we perceive the sensation as "blue", and so on.

The three primary colors of light are indeed red, blue, and green.  However, the three primary colors of *pigment* are cyan, yellow, and magenta, (check a color printer if you don't believe me).  This is due to the fact that pigments don't emit their own light.  They only reflect light selectively.

Magenta pigment strongly absorbs green light.  When white light (i.e., all frequencies) strikes magenta pigment, red and blue light is reflected, while green light is absorbed.  The red and blue light strike your eye and produce the sensation of magenta.

Likewise, cyan pigment strongly absorbs red light, while reflecting green and blue light.  Yellow pigment strongly absorbs blue light, while reflecting red and green light.

When you're dealing with light sources, the colors are additive:  red + blue = magenta, red + green = yellow, etc.  When you're dealing with pigments, the colors are subtractive:  white - blue = yellow, white - red = cyan, etc.

It's only the fact that we happen to have three types of cone cells each most sensitive to a specific color that makes any color more 'primary' than another.  Most birds have four types of cone cells.  Primary colors for birds would completely different.

Answer 2

Because the TV says so. If it's on TV, then it must be true.

Answer 3

yeah and i asked why 1+1=2 but i didnt have a answer that says good guestion...