I've never personally done a color run, but from talking with people who have I don't think you should be worried. It seems the color runs are much more social and fun vs a race - people like to get hit with the color, go back for more, go slowly through color areas to get more coverage. Or maybe they're covering their eyes and nose, so they walk through those areas
Several folks on these boards have done a color run though, so I'm sure they can give you better information
Personally, I'd be more worried about getting home without getting color all over the place!