how long is the tank?
Yellow labs and Demasoni always look cool, but you have to keep a good number of Demasoni.
The other things you might look at are:
Personally I think the yellow labs are beautiful but they are so common it's kind of boring. I like the activity of the Acei's and Demasoni, and the Rustys have a cool purple/brown look to them and are very playful.