Dave,
When I was the national sales manager for Flambeau Outdoors, I learned more about it than anyone should. I spent a good deal of time with one of the principals of Twilight Labs, the folks who developed, patented, and market the UVision line of paints. If you saw photos showing a gray decoy versus a white decoy on TV, it is merely an illustration or representation of the difference, not actually what a bird sees. At the SHOT Show in 2008, we set up a "Dark Room" with a UV light source and a camera that filtered out all available light except UV light. Most likely that is what you saw photos of; that type of photo. There is no way for a human to actually comprehend what the birds see, as their eye structure is different. We have red, blue, and green cone receptors in our retinas. They those three plus they have an additional cone that is sensitive to light from the UV wavelength, which we simply cannot see. The idea is that while ducks and geese do not have the ability to reason and deduce that if a decoy doesn't have the correct UV reflectiveness it is not a live bird, the response to correct UV reflectance is conditioning. If they live through decoying to incorrect reflectance decoys enough, they will learn to go only to live birds/decoys that exhibit the correct UV reflectance. To my knowledge, there has been no scientific testing of the results using UV painted and non-UV painted decoys. Getting an objective result, given all the other variables with waterfowl hunting, would be difficult at best.