Dark angels

Angels are known to be dead humans that have done good in their lives, and thus rose to heaven and obtained wings. Usually angels are shown in white, and most are messengers for some sort of god; angels are said to do no evil. Female angels are brought to mind most often when someone mentions angels.
[Copied from the Angels page]

Dark angels are almost the opposite of 'good' angels. They are still dead souls, but they have chosen a path of darkness instead of light. They are often shown in gray or black.