Ruby-throated Hummingbirds are bright emerald or golden-green on the back and crown, with gray-white underparts. 
Males have a brilliant iridescent red throat and black chin, but the throat may appear entirely black in poor light. 
Juvenile males resemble adult females, though usually with heavier throat markings.

The first 4 photos show a male; the last photo shows a female.

Los Tarrales Natural Reserve, Patulul, Suchitepequez, Guatemala, 18 & 19 January 2020