Your tank is a little small for putting more than 2 clowns in at the same time. If you put in a B&W female, she and the perc female will have it out until one (or both) is dead. If you put in a small male, he may get picked on until he's dead.
Color really won't matter in this situation. Clowns are territorial by nature and will defend their home against any other clowns that come near it. Some have gotten lucky with more than 2 clowns in a tank at the same time, but most do not.
If you really want more than one pair of clowns, get a second tank in my opinion.