Cones in the eyes have three main varieties (long, medium, and short wavelength absorbing photopigments) that allow for color perception.

“The cones come in three major varieties. At least for most people who aren't colorblind, you have so-called red cones, green cones, and blue cones. But they're not really red, green, and blue in the back of your eye. They are cones that either absorb long wavelength light, red, that absorb medium wavelength light, green, or short wavelength light, blue. The reason that they can absorb different wavelengths of light is they have different photopigments.”