Bfg tires letters turn brown

One thing I would like to mention is I have a 2012 Ram 3500 limited and two years ago I put 4 new BFG All-Terrain KO-2's on it. I tried Bleach Wite and a couple of others but really couldn't get the tires clean or the raised letters white. They are no means anything like we are seeing today as far a turning brown that's not the issue, the issue more road grim than anything. I pull a 36ft 15'000k 5th wheel and one year we were at a RV show and I saw this product call Reliable-1. I watched a demonstration on how it cleans campers and I was really impressed with the way the black streaks when sprayed with this stuff just ran right off. I bought a gallon to use on my camper and one day just for the hell of it I sprayed my truck tires. The tires look better than new and the letters are Pure White, I tried it on my BFG's with the brown letters but unfortunately it didn't work on them but my plan is to keep trying to see if it will keep them white now that I have them white using the acetone.