This is sort of too late, given that the OP already took his pictures... but there
are some things you can do.
Color runs are sort of derivative of the Indian festival of Holi, which is an incredible photographic opportunity--so much color, energy, and happiness! Holi is fun because it breaks down barriers and everyone gets to play a giant sort of mutual free-for-all tag. (Plus, I doubt it's any more dangerous than eating dyed Easter eggs or working in a kitchen when there's a bunch of flour in the air. If the organizer is good, it should just be food coloring in cornstarch.)
Especially if you have weather-sealed gear, I don't quite see why the cornstarch should necessarily be such a huge issue if you take some precautions. I shot my local Holi earlier this year with my K-r (which is notably
not weather-sealed) and my camera is no worse for it, despite the fact that I had people throwing colored powder at me for about six hours. I put my camera in a clear plastic bag (of the kind that sheets get packaged in, with some structural integrity and a zipper on one end) and cut out a hole in the bottom for my lens, in order to protect it from water and the majority of the dust. Some dust inevitably got in through the back of the bag with my hands, but less than I feared would. One thing I would say is critical, though, is a cheap UV filter--the filter I used still has a slight pinkish tinge. Because the bag was clear, I could still see through the viewfinder and my camera stayed protected
I also saw people who used underwater housings and rain bags--and one guy with a 5DmkII and a weather-sealed lens with no protection. He said that he'd been shooting Holi for five years and hadn't had a problem, but I'm not sure I could be quite that fearless myself.
I think you should pretty much be ok if you have a first layer of protection, a UV filter, and a lens you don't care too much about. You'll probably need to do some cosmetic cleanup after the event, but a few minutes with a blower and some Q-tips was enough for me. Or sit in a tree with a long lens. That works, too. I can see not wanting to risk your gear at all if your livelihood depends on it, but if you're taking pictures for fun...
Disclaimer: I'm no expert on the weather-sealing limit of cameras, so I could be totally in the wrong here. But Heie poured sand all over his cameras to no ill effect! I'd hate to see anybody pass up a fun photographic opportunity if it can be done safely. Cameras are tools to be used!
sgirvin's Album: Holi - PentaxForums.com