Violet Sabrewing Campylopterus hemileucurus, an incredibly brilliant violet or purple color, huge by hummingbird comparisons, and such a delight to see, has to be one of the coolest birds in the American tropics.
The males of this species have large white outer tail patches that alert observers to their presence, and probably make them more difficult for predators to track. They can look all dark, or black in poor light, but in good light when their irridescence is in full view, they are simply spectacular.
Often it is easiest to really study these guys at a hummingbird feeder, where they can dominate the scene, driving off smaller species at will.
If you get the chance to watch Violet Sabrewings, take the time to enjoy.
Good birding.