Cool pic. There's a PS plug-in
here that's great to get rid of green color casts that I use sometimes. There are a couple of dark spots on some of the stars. I find this can be taken care by doing a hot/cold pixel removal prior to stacking. Also stacking separate channels and recombining color in the end helps a lot with that - opposed to debayer then stack the color directly. You won't get as much color ringing due to mis-registration if you do it by channel.