other than the obvious dirt issues, there is one thing i would say...
this might seem a bit intense, but is relevant to bc riding, and could mean life/death- if you get buried in a slide and have a bit poking out, your buddy might not spy it if its white, whereas he'd see it straight off if it were coloured. this might seem stupid, and he should find you with his tracker, but sometimes a few seconds really do count!
anyways, hope that doesn't happen, but its a legit concern i think...