i would be careful. I added both at the same time to my tank (46 gal). all i had was rock, 2 clowns and a royal gramma. The gramma picked on my red firefish (Kotex) and he wound up getting red bruises under his skin. He then dissapeared. I still have my purple firefish to this day and he is out a whole lot, except for when he's getting picked on by the other fish. He is real skittish though.
just be careful that the 2 firefishes are getting along cause i dont htink you're supposed to get both in 1 tank