BF Goodrich radial T/A white letters

I bought 14's and 15's at the same time. The 14's on the front never did turn brown, Noting but issues with the 255/60-15's on the rear. I tried many different whitewall tire cleaners. No good. I had to grind the letter surface to get them white and they would turn brown within a month.
Mike - have you tried the acetone?