Its a tough one I know. Trying to pick a colour combo can sometimes be harder than picking the boat itself. Here's a link that I found quite useful when deciding which colours to go for:
Only thing is the guy who wrote this was talking about PU tubes which don't really fade, compared to Hypalon so you will have to take this into account if you are getting a Hypalon boat, avoiding colours that will look terrible faded.
I've gone for the blue tubes/grey hull combo you see in the link. I personally think the boat you see with the yellow hull/grey tubes looks very smart as well. You could always have contrasting bright wear patches to make the boat more visible. At the end of the day it comes down to what YOU like so we can only advise. You have to make the hard choice.
Oh god you haven't even decided what rib you want and I've probably gone and got you alll worried about colours. Sorry!!