When I did my faux stained glass window (see below) I used hot glue to do the "lead" outline. It worked really well on glass because although it sticks very well, if I made a mistake I could remove it with a little effort. (And it was easy to remove the little strings of glue you always get when using a glue gun by just pulling them off.)
Next, I painted the dried glue with black acrylic paint. It was a little tedious but I switched to using an oil paint pen for touching it up and that worked pretty well too. This gives you the opportunity to make your glue lines look much neater, because you can pick and choose which of them show by which you paint black.
Then, to fill in the areas in between the lines of black I used more cheap acrylic paint mixed with Elmer's glue and a bit of water. The ratio wasn't exact, I just experimented until I got a consistency that was fluid enough it sort of flowed into the empty spaces. The Elmer's glue makes the acrylic paint translucent and look a lot like colored glass. You can build up however many layers you want, increasing the opacity.
Finally, I sealed with a clear Rustoleum spray paint and hung it up in my window. It has held up very well in direct sun for the last few years, I attribute the paint not cracking most likely to the elasticity from the glue.I hope this technique will work for you!