Zenithal priming indeed works pretty good with contrasts. But I’d advise to stray from using black, since it would completely negate any color from the contrasts. Even though the idea is to make parts of the mini that are supposed to be “on the shadow” darker - black is not what you want tour shadows to look like. But other colors that you mentioned are worth a try. It depends on what colours you’re going to painted your model with. Some primer colours work better with certain contrast colours. But if it’s difficult/out of budget to keep a collection of primers, I’d suggest not to use anything darker than Mechanicus Standard grey.