Here's my takes on several colors I've used...
Yellow: looks poor REALLY fast. Any little bit or dirt or grime is immediately noticeable.
Blue: Too much when you got to town with it. Overpowers the senses.
Orange: As bad as yellow and blue combined.
Cast Iron: Kind of a cool look, but looks "fake" when used extensively.
Black: looks good, but you can't see squat.
Machinery Grey/Ford Grey: I like it. Good visibility for leaks, and easy on the eyes. Some grime and dirt won't destroy looks. Another color I like is the tan color used on Cummins engines.
"Hammerites": same look in all colors, but works best on things you are trying to make look "old". A buddy painted his frame with it, but he used blue. Turned out nice, but Blue truck, blue frame - too much blue. I would avoid paiting drivetrain with it.
'91 V3500 Crewcab, bobbed, SM465/NP205, D60/14FF, 4.10, 12k Warn, dual batts, 2" body, Blazer fuel tank.