That's just because the vegan leather doesn't breathe like real leather does. Nothing to worry about. It's actually better with the white interior, because it's softer and creases more than the black.
I've had 2 TM3 (so far), white is definitely nicer to the touch and from a comfort perspective.
Exactly what I figured. It's not breathing, and the ol' back o' the knee gets a wee bit more sweat. Not a huge deal, but I would prefer leather if given the option.