"UV Theory" is mostly that... A lot of theory...

As a chemical engineer, I worked in the past with renewable resource and biodegradable 'green chemical' replacement products for synthetic UV brightners in laundry detergent. The spectral analytical tools we used to pressure test the products against the brightening agents used in existing commercially available brightening detergents is the same technology used in the "here's the proof" photography for "UV FREE" hunting washes and clothing.

Here's where the theory breaks down

First, recognize that all "color" on Earth is really only a matter of a physical property of the material. The item is not ACTUALLY that color, but rather the atomic or molecular structure of the item REFLECTS a certain spectrum of light and absorbs others, which causes our eye to view it as one specific color.

Therefore, a color can ONLY appear if there is light in its reflective spectrum emitted upon it. In other words, if I shine a red light on a mirror, it can only reflect a red light, never a green, and vice versa. If I shine a UV light on a red shirt, it will show up black, because it cannot reflect the UV light. Anybody remember "blacklights"???

Energy from sunlight comes to Earth emitted in different wavelengths of light. Depending on the study you read, only between 5-10% of the sun's energy is emitted in the UV spectrum, and ONLY UVA and UVB rays reach the surface of the Earth, as the high energy, ultra-short wavelength UVC spectra are completely washed by the Ozone Layer. The majority of UVA makes it to the surface, and only a portion of the UVB penetrates - arguably around 50% of it's total energy. Between 40-50% of the Sun's energy is emitted as "visible light", which is not scrubbed by the Ozone Layer. So if we vaguely assume 7% total UV, broken down into 3rds, kill the UVC, and half of the UVB, that's about 3.5% of the total energy.

Now, there are UV sensitive chemicals, which is what we use in UV brighteners, that reflect UV which help increase the overall reflective energy of a given material. The idea here is that it adds "brightness" to colors by increasing the total light reflected by the object.

So on a relative basis, visible light is somewhere between 5-8x more powerful within the total light spectrum as UV light.

Say it's a red shirt, and reds make up about 10% of the total Visible light spectrum. Assuming 45% visible energy, that's 4.5 units reflected on a red shirt. Add in the UV brightener, which isn't fully visible to the human eye, you gain about another 1-2 "units" of brightness on top of the Red Energy. Boom, brighter shirt.

Tying this all together:

On Earth, which is where most of us hunt deer, the visible light spectrum will always dominate the total light reflected by a given object.

IN LAYMAN'S TERMS - UV intensity is much weaker than Total Light and Visible Light intensities.

Consider this familiar experience: 20-30yrs ago you walked into a college party. The lights were on. You were wearing a black cotton shirt. Your shirt looked black with the lights on. But your buddy flips off the lights and suddenly the room has a blue/purple hue, your teeth look like they are glowing, and your black shirt is COVERED in white flecks. The cotton has natural UV reflectance, so every little fuzzball, pill, or knap on the shirt glows under the blacklight.

When the lights were on, the visible light spectrum dominated the exposed color, so you couldn't even notice the flecks, or your teeth.

THIS IS HOW OUR SUN WORKS. Even in dusk and dawn, Visible Light dominates the color as seen by animals. Some animals can be more sensitive to UV spectra than we are as humans, but deer still have a higher sensitivity to visible light than they do to UV light. THEREFORE, in the presence of visible light, they will see colors based on visible light colors, NOT based on the UV spectra. Colors will be brighter for them than they are for us, because of their higher sensitivity to UV "brighteners", but it's not a dominating light energy.

So no, "UV Theory" is nothing more than misconstrued and ill-applied science. It's like turning on your headlights during the day, nothing more.