I was wondering about adding the ability to change the usergroups colors and displaying a legend at the bottom with those colors you chose as your usergroups? Makes members feel extra special.

Change the user group colours where?

each usergroup already gets a unique style applied to it... so you could change background of their posts or user info area to show their usergroup membership... that could get tricky if multiple...

you could also style the usergroup name display based on the style... then insert your own legend wherever you like - it would just be static html, right?  only change if you added or removed usergroups...