I always use white shoe polish since I read tires more than rely on a pyrometer. Basically, as long as you are getting a nice, even wear, with the tire rolling over nicely, the tire is working as it should. If it looks like the edges are rolling rubber more than the center, you need to bump the pressures a pound or two, and if the center looks like it's been spit-shined, you might be running pressures too high. Of course, a pyrometer will tell you the same thing, but I'm kinda used to tweaking setups on slicks with little time to heat them up and measure