Primary colors: primary only for us Q: Why are red, green, and
blue the primary colors? A: What we call "primary colors" has
nothing to do with the nature of light. It depends rather on how
we humans detect light. "Color really refers to a sensation that
a particular wavelength of light [produces]," says Brian
DeBroff, ophthalmology professor at the Yale School Human eyes
have two types of cells for absorbing light: rods and cones. You
see little color at night. Consequently, the rods, used mostly
for night vision, detect primarily light and dark. The cones
detect color and favor some colors over others. They absorb
blue, green, and red light best. That's why those colors are
called "primary." We perceive white when the cones absorb light
containing equal amounts of the three primary colors. By adding
together primary-color responses, our eyes see almost any color.
How do we perceive light at all? Special pigments in the rods
and cones absorb light energy and change it into chemical
energy, which, in turn, st