Hey Dick Sable, Yea, the UV brightners are a big deal. Rutgers, and a few other colleges/Universities have done studies on UV brightners and animal perception or recognition.
all of my hunting cloths are Predator camo, cotton, no UVs added. THere are a ton of videos and websites out there that show clothes in UV light, and they light up like neon lights. It's crazy. Yea, that makes a big difference.
You're also right that old time wool clothes are made without UV brightners. That's why they still work great today.