Black absorbs heat, making all the delicate electronic components inside hotter. Electronics don't like heat, and tend to fail when things get too hot. This is why this is a bad idea (from an equipment standpoint).
If OP lives in an environment where ambient temp never gets too hot, no biggie. But in hot sunny climates, this would most likely at best shorten the lifespan of the screen, and at worst cause outright failure on a hot summer day.
