We can't force someone to use their own color or anything. They really have the right to do whatever they want. If you're seeing this problem, though, you may want to talk to one of the ops or the channel founder about using channelmode +c. The mode prevents any user who isn't +q/+a/+o/+h/+v from sending messages to the channel containing control codes (which includes colors). Or perhaps, you could suggest to the people in the channel about using their own colors so that things don't get as hectic.
Hope this helps,