Here's my current and up-to-date reference sheet. Figured I might as well upload this here first before all the art I've gotten with it :P A tremendous thanks to Adalfyre for putting this together and for being so easy to communicate with. If you're not watching her, go do that now! Anyway, I've managed to include a bunch of relevant information that I couldn't on the last one, especially backstory/world lore related. Also, detail wise, I feel this is a much better representation of Jarren and does a much better job of capturing the image I have of him in my head.
Full res here: http://i.imgur.com/wC26Via.jpg
Artist's page here: http://www.furaffinity.net/user/adalfyre