I'm in the temperate Pacific NW, so snow or sub-freezing temps is not a particular factor.  So far I have not had any predator problems, although winter will be a different story.  I was thinking of an almost black tint to the plexiglass, just enough so I could make out a body shape.  I do occasionally get very clever raccoons, but I think the design of the nest box is such that the coon would have a difficult time getting any sort of leverage to open the lid and be able to reach inside.  I may be wrong (I have been before with those critters) and may have to install a locking device of some sort.  We shall see. I'm in a rural area and my potential predators are coyote, coons, possums, eagles, and hawks.  So far, I have been able to leave the coop door open when we are gone for weekends with no problems.  I usually, but not always, close it at night when we are home.  Kind of backward, but I'd rather not leave the chickens cooped up all day when we are gone.