I finally figured it out...Purple color scheme, going to a lurid pink as his power increases, lots of spiky bits, ascending to a chaos god avatar gives him more chrome bling and horns, a tendency towards overdrinking and other substance abuse chasing that power, a love of family that slides into the blatantly self-destructive...
Galvatron is Cybertron's first Slaanesh devotee and he doesn't even know it.