Black is great if you want to make it hard to see a leak or problem.
Bare aluminum is great if you like fingerprints & stains for that patina look.
My racecar motors get a light industrial grey - learned that from the ex-Penske TA Javelin I worked on - aluminum included.
Everything else gets the appropriate factory color, and I like to downplay the hot-rod items; that started back in the street-racing days...
Not saying everyone who doesn't do what I do is wrong, though; just 'splainin' my logic...