This was the effect of taking an HDR photo with the iPhone's built-in camera app. (It's not exactly like normal HDR; it seems to take two photos at different exposures and combine parts of them.)

Because there's a small amount of lag between when the first and second photos are taken, the camera picked up different colors from the flashing lights. The non-HDR version of this photo can be seen in my "Scraps" section.

Taken at one of the dances at Califur 2011.