From behind the lens of his camera, Michael McNulty became curious about the rich colors of the desert, so he began to research the properties of light, and how the human eye sees color.

"One way to define light is that it’s the part of the electromagnetic spectrum we can see," McNulty said. "But that’s a really tiny, tiny portion of the whole electromagnetic spectrum."

PHOTO: Michael McNulty

The human eye can see less than one tenth of one percent of such, mostly, invisible spectrum, which includes ultraviolet rays, gamma rays, and x-rays.

To see color within the visible spectrum, most humans have three sorts of light receptors in the retina: a set for red, a set for green, and a set for blue.

These light receptors, called cones, send signals to the brain, which when combined are interpreted as all colors of the spectrum. Three-coned, or trichromatic vision is actually rare for mammals. Typically most mammals, and some so-called colorblind people, lack the cones to perceive red wavelengths.

However, McNulty's research shows that even with three cones, not all colors are seen equally.

"We don’t necessarily think we have trouble looking at red and blue, but if you try to look at different shades of red and blue, you’re going to find that you cannot distinguish them as well as you can green," McNulty said.

McNulty shares his stories of red, green blue in this segment of AZ Illustrated Science. He is working on a book based on his research about the colors of light.