Ya I donno about the heat gun! I'm contemplating a press from watchbitz, that should do the trick! I'm also looking for a professional glass stain, I found one on a Italian website but it's not set up to ship outside the country if I'm not mistaken
http://www.amicucci.it/colori.aspx?c=4&s=437
The press will help you get the whole shebang back on a lot easier, I can tell you that. It was pretty easy for me to get the bezel to pop off with a razor (and then just lift the crystal and gasket off) but you gotta put the whole thing back as one unit, and you gotta do it with even pressure around, so that took me like 20 tries to do by hand.
Regarding the color , I couldn't find a way to order anything like that to the states either, so I used a green sharpie to color the edges, let it dry, then went over it with a clear acrylic sealing pen. That came out pretty good.
Edit: BTW, heat gun would work, but it will work because youre deforming or flat out melting the nylon crystal gasket
So if you want it waterproof after it's not the best choice.