QUESTION: Are deer completely color-blind? I've always been told they are, but I read comments in the July 29, 2013 Ask the Biologist about deer in the headlights and you mentioned colors. If deer can see certain colors, it might change the way we hunt. - Nivia W.
ANSWER: Much of what we know about deer vision is attributed to researchers at the University of Georgia's Warnell School of Forestry and Natural Resources.
They've actually implanted sensors in captive deer to record which wavelengths of light stimulate brain activity.
They learned deer have only two classes of cones (color receptors). Humans have three. They determined that unlike the trichromatic (three-color) vision of humans, deer vision is most sensitive to short wavelength (blue-violet) and middle-wavelength light (green-yellow).
Also, their lenses lack a yellow pigment found in the human eye, which filters out ultraviolet light almost completely, and absorbs it strongly in the violet and blue regions.
As a result, a deer's sensitivity to blue and violet is much higher than that of ours.
Their sensitivity is lowest in the spectrum of yellow-green, green, yellow, orange and red.
To them, orange and red appear only as different shades of gray, which is why they aren't alarmed by most hues of blaze orange.
When spooked, it's often because the movement of a solid human form catches the deer's eyes, rather than them noticing color.
It's important to note that blaze orange is pigmented in two ways. One is by combining red and yellow. The other is by combining yellow and magenta (reddish-purple). Magenta is in the peak sensitivity range of a deer's visual spectrum, and thus will glow in a deer's eyes.
Be aware that many conventional laundry detergents and color dyes used on camouflage clothing manufactured overseas contain brightening, blueing or whitening agents.
These collect light energy from a wide range of wavelengths and re-radiate it in a powerful peak at a range of about 440 nanometers - near maximum sensitivity of a deer. They might not see it well in bright sunlight, but in twilight these brightening agents can make your clothes glow like a neon sign to deer.
The folks at ATSKO, who sponsored some of the early deer vision research, created a product called U-V Killer. When properly applied, it counteracts the effects of brightening agents, taking reflected light out of the deer's more sensitive visual regions.