There are a few schools of thought on this topic. Some say that tan sidewalls are indeed less durable than white walls or other colored sidewalls. The thinking is that the darker color absorbs more heat, which can lead to premature tire failure. Others believe that there is no difference in durability between tan and white sidewalls (or any other colors, for that matter). The only thing that might affect durability is the type of rubber compound used in the tires. So, if you're looking for maximum tire life, you might want to stick with white walls (or another light color).