You can change the skin colour of the editor to match your site very easily from within the HTML Editor settings when inserting it into a page. However, you may want to wait a little bit before taking the plunge with the upgrade as there appears to be a serious bug in HTML Editor 3 relating to the use of custom styles - see this post for details showthread.php?t=18408
I'm hoping to get an answer to the problem from WebAssist on Monday (I'm assuming they don't work weekends).