I have no particular view on which colour to choose, but......... on the visor front......
My Geckos originally were bought with full-face visors. I found out though that when I really needed to wear the helmet, it was invariably at a time when the muck and bullets were flying, and that with my increased breathing and talking rate, the visor easily steamed up. And who can be bothered to keep coating the visor with Holts whatsitstuff? Raising it slightly, as Louise suggested, never really worked from me as the next slam down of the boat would cause the visor to snap shut, and so we went round the loop again.
Eventually I had one helmet changed to half-visor and have never regretted it. The main purpose for me is to maintain visibility. Oh all right, all right, so as I can carry on smoking at the same time then, as well.
But one good piece of advice from Louise though is definately to keep your studs greased. You never know do you?