so i used the destiny theme to practice some inner and out glow effects and here is what i got.
and i also used this one to try out as a type of pop out. i made this with bunny's advice and wanted to take a stab at the style of a pop out but i like how its not a strait hard edge border like most sigs
The latter is much better in my opinion because it shows more depth. The first seems flat and looks to have a bit to much glow. I would need you to send me a screen cap of what your tab looks like so I could try to explain it more relatably to gimp, but I usually leave my spread low and my distance higher. I also drop the opacity of the glow so it's see-able, but not notable at a glance