If it helps any: Most older cars have a distributor cap made of bakelite/plastic and they're usually brown or black. Some aftermarket ones might be different colors, but it's up to you. Heads are usually engine color, but can be bare aluminum or steel. I've done a couple of engines where the engine block was aluminum and the head/valve cover was black. Transmissions vary as well. Had a 1:1 1972 Buick where the engine/transmission were red, but we ended up having to replace the tranny with a junker that was blue. I normally paint mine steel or aluminum. This is all subjective depending on your own style. Car interiors are a whole different ballgame. Your best bet there is to look online for reference pics and find a color combo you can live with. That same Buick was orange with a white vinyl top, seats and upper door panels, black carpets, lower door panels and dash with wood trim. Sounds weird, but it was a beautiful car back in its day.