It's the rods and the cones, you see

For those not keeping up with the comments, Jason provided an excellent answer to my question about why hunters bother with cami clothes when they're wearing blaze orange hats (per Virginia law):

"Deer see light differently than we do. While they can perceive color, most of what they see is black/white/grays. Their vision is primarily geared towards nightime vision - and the portion of vision that works best in the dark is the black/white portion, or the rods. They do have cones in their eyes to see color, but their color vision is optimized for different wavelengths than human vision. Deer don't have that many red cones, so they hardly see the reds/oranges.
In the end, the best way to think about a deer's vision is that they see shade contrasts, not the color contrasts. So even if I'm wearing a blaze orange camo coat, the deer would see the shading of the camo, not the orange. But, the blaze orange is needed for other hunters to not mistake you for game - and each state has laws regarding what you must wear for blaze orange while hunting."

Thanks, Jason! Another of life's mysteries solved.