I have much to learn

[Maccwar]

I found something similar to what I'm after.

http://www.cartographersguild.com/showthread.php?t=4107

Now to try and get those effects in GIMP rather than PS.

[Karro]

Do you have each region of color on a separate layer in GIMP?

If so, then, yes, I think you can achieve this with masks. For each color layer, you'd have a layer mask that defines the border of the region. The outside edge of region would be represented on the layer mask by a hard line from black to white. But the inner portion of the region would be a fading gradient of some sort from white back to black. If you want most of the inner portion of the regions to be the background color, you'd fade to black on the mask relatively quickly. If you want the fade to be longer and more subtle, likewise with the mask.

Does that make sense?

[jfrazierjr]

There are several ways to do this, but Karro is right in that layer masks is the "correct" way in that it's non destructive.