Hi and welcome!
As others have said, any type of tang is out. They need BIG tanks because they have to swim so much.
Check out firefish. There are red and purple firefish, and those would be good for your tank.
Maybe a few green chromis? They have a nice turquoise color.
Also, the sixline wrasse is very colorful.
Maybe a coral beauty or flame angel.
Those are the fish I'd recommend you look into.