The only thing might suggest is to have slightly smaller circles for non-Rock & Crystal crew. Just maybe 1.5 times the size or something. But they look fine as is.
IN OTHER NEWS!!!!!!!!!!!!!!!!!!!!
Check this mod out!!http://www.ftlgame.com/forum/viewtopic.php?f=11&t=24541&p=77291#p77291
It changes the portraits for crew!!!!! Apparently portraits are not the first frame of the walking animation. They are actually in the bottom left of each sheet!!!!! So now you can finally do what you wanted to do with adding new portraits. The person who made the above mod did a really good job, BUT, I would like to see what you come up with because I think your sprite work would match the vanilla style more.
Also, it might actually be possible to make the portraits animated but I haven't checked that. If it is you could just make them blink like it all the RPG games.

This also opens up some good possibilities for Lighter Than Air.
