Totally different temperments. Grammas are pretty peaceful, unless they are cramped in small quarters with other grammas.
Royal (Bicolor) Dottybacks (Pictochromis) are hands down, the worst of the small dottybacks. They can be real terrors!
Matthew
I assume the OP knew this & wanted to know how to seperate the two species. Aside from what's been said, Dotty's have a slight dent in their eye that makes them look mean & aggressive..