Well, if they are in a rack that is closed off on 3 sides, then they are going to be pretty darn secure no matter what color of tub you use...

And on the other hand, from personal experience: I use clear tubs that are exposed to ambient indoor light. My skittish BP doesn't even like to use his [dark] hides - he prefers to ball up in the corner of the tub under some newspaper. He doesn't seem to mind the light coming in. But this may vary from snake to snake.