Reddit reviews A Natural History of Seeing: The Art and Science of Vision

Eyes are complicated, but basically, they don't detect every color individually. Your eye has three sets of cones; ones that detect the blueness of the light that hits it, ones that detect the redness, and ones that detect the greenness. If the light reaching a green cone has a wavelength that's near green, the cone sends a message saying it has greenness. The closer the light is to the ideal green, the louder this message is. For mixed colors like yellow, the green cones send a loud message, the red cones send a medium message (since yellow wavelengths are closer to green than to red), and the blue cones send a whisper or don't speak at all (since yellow is closer to both green and red than to blue). The brain then interprets this arrangement of volumes as the color yellow. The brain interprets near-equal volumes in all three cones as colors in greyscale. If the light is bright and equal, it's interpreted as a shade of white. If it's dark and equal, it's a shade of grey or black.

It's really a lot more complicated than this. You should pick up a book on eyes and vision. It's interesting stuff. I'd recommend A Natural History of Seeing.

That was awesome. I'm reading A Natural History of Seeing so its especially cool to see footage illustrating what I just learned about.