Black eyes aren't really black, they are actually a very dark brown, so technically, it is impossible to have black eyes. unless your talking about the the bruise yes people can have a black eye...
Any blow in the area of the eye can cause the bruising and swelling associated with a black eye. It sometimes doesn't take much to break a number of the small blood vessels and create the nasty...
A black eye is just bruising around the eye. All you can really do is apply a cold pack to your eye to keep it from swelling too much. The bruising should go away after a few days to a week.