Hi Dave;
I have found that certain mfgrs. get it right. There many old Monogram models sitting on my shelves. Factory stock and no paint. Why? the molded color was so beautiful, cleanup and polish was the order of the day. I always did paint the interior of the bodies to solve transluscency problems but that was force of habit not need.
I have noticed though-Don't laugh please? Take Tamiya, Hasegawa and Monogram models molded in black. None of them are the same color! This happens when the base color is predicated on the Red, Blue or Green base of the color spectrum, there's also a base Blue takeoff that seems purplish in certain light. That's the technical side of it. If the molding is good, you like the color, then leave it alone if YOU wish, It's your Model! Right!?