Basically? You wear white, you run 5K, and at the end of ever kilometer, they shower you with colored powder! (I'm pretty sure it's dyed cornstarch?) Each kilometer is a different color so by the end, your a pretty little rainbow mess! And then to top it all off, there is a color celebration at the end! They have a stage with a DJ and then every 15 minutes they toss out color packets (they gave you each one at the beginning but you could buy/catch/beg for more) and then you all cut lose at once - my all time favorite part for sure. :)
There was over 25,000 runners that day - so many people!!! They sent you out in groups of a couple hundred - we lucked out and were in the 3rd group so we didn't have to wait around the entire day!
Here are a few photos from the day!