I reinstalled my system with the Ubuntu 9.10 beta a couple of days ago and today I noticed that any video that is played has a weird blue tint to it.

The video plugin that's installed in Karmic is gstreamer by default, and that has a configuration tool called gstreamer-properties which can be accessed from the command line. I found that if I changed the Default Output on the Video tab to "XWindow System (no Xv)" videos played in normal colours.