UI Skins at Lunch of Green Server
 

I have a question about which UI skins were available at the start of the Green server. Was duxaui available at launch or did that come later? Was it just default and default_old then velious and duxaui came later?

I don't play on green but my understanding is that you could use any UI you wanted from day 1.

Yeah there is nothing stopping anyone from making cosmetic changes to their clientside experience. The game isn't patched. There are checks for the important things to make sure they match the server, and won't allow you to log on if you alter anything non-cosmetic.