I'd just like to add a very brief cloaking tutorial.TaxiService has one for Photoshop.
For GIMP, I do something a little different.
To recolor the lines, first do a color-select on all the black outlines (000000), with low threshold, so it only copies lines and not shades of black similar to lines. Paste the selection onto a new layer. Then color-select the lines again, go to the bucket tool, and change its fill mode from "fill similar colors" to "fill entire selection"--in this case, it'll fill your entire color selection.
Then I use this guide
for the outer glow. I used blur radius 15, and I used FFFFFF for the lines and 00FFFF for the glow.
EDIT: In the case that you can't get all the outlines, this is what I do instead.viewtopic.php?f=12&t=17442&start=330#p87933