Im somewhat in agreement with meegosh, though I wouldn't put them in anything smaller than a 20 long or 29g. I had zebra danios in a 10g, then moved them to a 55g. Man, they zipped from one side of the tank to the other. They definitely deserve more room than most people give them.
As far as colorful for this tank... Hmmm. Tetras in general are pretty active fish. Neons and cardinals are pretty popular fish, though cardinals would be my suggestion over neons. Lemon tetras, harlequin rasboros, maybe some type of platy. Do you have any idea what type of fish, or what color you're looking for?