You're probably thinking of the whole "UV Brightener" thing. Apparently some dyes and detergents nowadays have whatever a "UV Brightener" is in them.
They're suppose to show up to deer like a blue version of our blaze orange.
Personally don't buy it, but many do.
Easy way to test for these brighteners is to go into a dark room with your gear and turn on a UV black light. They'll glow like a t-shirt at a dance party if they've got the brighteners.
Never tested my stuff personally. Don't want to buy the light...don't want to "need" new clothes...and like I said..."Personally don't buy it."
Sorry that got long-winded