Either white, or use a grey primer. With a lot of the prop work I've done in the past, I find the grey works a lot better for really bringing out any imperfections that need to be fixed.
Liking what you've done so far with the new helmet, buddy. That's startint to look "as smooth as an android's bottom" (please don't tell me I'm the
only one who knows what that line's from, lol).
Okay... so maybe that was a little too much on the geeky/nerdy side. Sue me
Btw, the brim details on your new helmet... are those recessed?