It takes time, but the best dome tanner is just the sun. It won't happen over a few days or even a week, though, and don't of course get it sunburnt
My dome has gradually become darker over the two and a half years I've been shaving. Even now, it's a little lighter than my face: that's just natural, especially where you still have hair growth.
Some of the guys do use self-tanning products. I would say the ones that naturally promote tanning are the best, rather than fake tans.
