Well primal Dialga isn't actually "primal" in the same sense that Groudon and Kyogre are in ORAS. I'm not sure if it was a translation error but Primal Dialga is actually supposed to be named "Dark Dialga" (Japanese name). Pretty much the difference between Dialga and primal Dialga are it's motives I guess. Dialga wants to maintain the balance of time whereas Primal Dialga is just bat shi* crazy.
Though Primal Dialga still has the ability to time travel, it has lost control of time. It pretty much loses it's mind and goes into deep rage caring for nothing but the preservation of itself. You said not to mention color but the colors actually demonstrate its state of mind, not primal reversion. The diamond in it's chest is bright red/orange to demonstrate its loss of control. Primal Dialga's logical reasoning goes straight out the window and he actually tries to stop the flow of time which is a arguably the biggest difference. There isn't much more to it as far as I'm concerned.