Venison.
They see reflected UV off our clothes from optical brighteners in the detergent, so we glow like a lightbulb under sunlight to them.
The color vision of many nonhuman vertebrates differs from that of humans in several respects. Most notably, many mammals, including deer, pigs, cows, other ungulates, rabbits, squirrels, dogs and cats have only two populations of cone photoreceptors compared with three in humans.
Pigs, for example, have two photopigments with absorption maxima at about 440 nm and 560 nm (Neitz et al. (1989), Visual Neuroscience 2: 97-100). These species are said to possess dichromatic vision. Dichromatic vision results in a very limited color perception compared with trichromatic.
Whereas trichromatic humans can perceive several hundred color gradations from different wavelengths in the visible spectrum, dichromatic animals can perceive only two distinct colors with gradations of colorlessness in between.
Thus, at low wavelengths of incident light, a dichromat perceives a blue color. As the wavelength is raised, the intensity of blue color decreases. Eventually, the blue color completely disappears and the light appears entirely colorless. On further increasing the wavelength, an increasing intensity of yellow appear, until eventually the yellow light appears relatively pure (i.e., saturated).
The wavelength at which light appears entirely colorless, untinted by either blue or yellow coloration, is that at which the two populations of cone cells are equally stimulated. This wavelength is known as the neutral point.
The colorless light, at or around the neutral point, is perceived as white or a shade of gray, depending on its intensity and the background illumination.
A further notable difference in vision between many nonhuman vertebrates and humans, is that the former lack the human's yellow coloration of the lens of the eye. In nonhuman vertebrates lacking the yellow coloration, short wavelength blue and ultraviolet light that would be filtered out in humans, reaches the nonhuman's retina.
Thus, some nonhuman vertebrates have much greater sensitivity that humans to short wavelength light.
The rest of the lengthy article describes techniques for camouflaging the hunter, as opposed to camouflaging the soldier.
Camouflage Materials