I missed one of the important details. After seeing the pink, I pulled up the paper towel and checked the temps in corners and things more thoroughly. I did find a few spots right in the corners where the tub has a groove around the edge with temperatures as high as 105. Is that high enough to cause burns?

My first thought was shed cycle, too, but the pink doesn't go all the way up their bellies (anywhere from 1/4 to halfway up, I'd say). Is that normal when going into shed? And it seemed strange for all four of them to show the color at the same time. Also, they don't particularly seem like they're going into shed - eyes are clear (except for one girl ) and colors seem pretty sharp (again, I've only had them for 48 hours now, so that's hard to tell).