Every character gets assigned one six generic palettes if they don't have unique models. The traditional Blue, Red and Green. Black, Brown and Yellow(ish) for males. Pink, Yellow and Brownish for females.
As for the overclass, the way the games assigns models, animations and palettes IS would have to use a hacky method to assign it to them. A method which I don't think IS knows about and I'm not sure if it still works from Fates(they use the same file so I'm assuming it still does).
Could they have made unique palettes for everyone? Probably. It's just that they chose to do an easier, quicker and cheaper method. I'd say it's a step up from Fates and Awakening since everyone isn't just a generic blue.
That's not unique palette. It's the red one.