Keeping your carboy out of direct sunlight and out of strong fluorescent light should be fine esepcially if it's a translucent rather than transparent carboy, but if you're really concerned, warpping it with a dark towel should be enough.
I've never had a problem with using white plastic buckets, a week or two in the middle of the sunny kitchen never seemed to hurt anything, and my carboys sit under a countertop (equivalent to a cupboard with no doors), and my wine shelf is directly in a window so I've hung a tablecloth over the half of the window that might shine directly on the wine, but I've never bothered covering any of my carboys specifically. One of these days I'll split a batch and leave one in the sun to see what it does to the taste...