what kind of tangs?
I have a yellow tang who has really brightened up my tank. Always swiming and investigating rocks and power heads. Just about everyone who's come over since I got him has exclaimed, "man, thats a bright fish" I also have a couple of Blue Chromis that are very active non-agressive fish. Perc clowns always add a nice dash of color and some have been known to host corals when an anenome isn't resent.
If you're looking for livelyness and color, i would say more smaller fish rather than a couple larger fish. Will make the tank a little more active. I say, a school of chromi's