Had that issue on my Camaro. Bought the tires around 2016. It took about a year for the rears to begin turning brown. I was able to clean each individual letter with acetone, but that was crazy. The fronts stayed bright white. 2 different size tires. After Googling the issue, I realized others had the same problem, so I went back to the shop I purchased them from and they filled out a special form that went to Michelin who owns BFG. They honored the complaint and replaced them. Now after about 3 years, they’re doing the same. The fronts are still perfect. BFGs were on my Monte when I bought it. As Glen said, time will tell.