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Red is probably the best for visibility, but... er... um.. I think I'll go with blue :)
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Make sure you bring along someone in a red one though, so the drunk drivers will know who to aim at. 

(I know, that was terrible)
Actually, yellow would be better than red for visibility. (And longevity, obviously.)
Yeah, red is actually horrible for visibility.  The reason "old school houses" and firetrucks were painted red was it was the cheapest paint at the time, generally.  (So goes a lot of the myth, anyway; but makes sense, neither of these professions paid well, or at all.)
I'm buying the "Disposable Crewman" shirt for my son!