Toby: Do your camera fog inside the case or outside? On hot days, I suppose you can get fog on the outside of the case. If that happens, I think the new black GoPro will bee setter, as it will heat faster by the sun.
Fogging happens when humid hot air comes in contact with a cooler surface. The hotter the air, the more water it can contain. When the air cools, it will loose its water. So if you trap hot air in the case, and cool it by dunking it in water, the air inside will loose water onto the cool surface on the inside of the case. If the outside air is hot, and you cool the case by dunking it in water, the outside air will loose its water onto the cool surface on the outside of the case. If the camera is black, it will heat faster by the sun after a dunking, and therefore not fog as much. That is my hypothesis, and I'm pretty sure I'm right.