...most of them are black, and they absorb heat very quickly. Had my P-rod pumped to 3000 and sitting in the sun it went up a couple hundred psi in no time.
Way back when I was a competitor in FT matches we all has issues with hot sun making shifts in poi.. my solution was to paint my gun case white, and added a cuple air vents on the sides. Tested with a thermometer the case was almost 20 degrees cooler than leaving the rifle out in the sun. Made a hugh dfference!!