Royal Gramma

Snapshot: Its stunning coloration, iridescent purples merge seamlessly into golden yellows. A sleek black line runs from mouth to eye. A small spot adorns its dorsal fin.
 
Other tidbits: Can grow up to 7.5cm or so. Range extends from the Caribbean region, from Florida to the northern coast of South America. 
 
Bare bones must know: Any tank system without aggressive fish.