First of all, this is pretty much for supernatural icons, because they're always so dark :)
1 Crop your base to 100x100 pixels for an icon size if you wish.
2 Duplicate your base and set it to Screen at 100%.
*This step is optional, only do this if your base was really dark like mine was*
3 Make a new Color Balance layer:
Shadows: -20, -8, -9
Midtones: -13, -5, -21
Highlights: +14, -7, +17
4 Make a new Fill Layer with #1d0000 and set it to Exclusion at 100%.
5 Make a new Channel Mixer layer:
Red: +94, +4, -2, 0
Blue: +8, -8, +98, +4
6 Make a new Fill Layer with #00001d and set it to Exclusion at 100%.
7 Last step, don't forget it, it's very important!
Make a new Brightness/Contrast layer with these settings:
Other icons made with the same coloring (with a few minor changes, i.e. no screen layer):
Also, I got the picture here: http://www.supernatural.tv/pictures/displayimage.php?album=171&pos=418
I'd love to see comments and your results!