Thanks for the responses guys, but I'm very much a beginner with Gimp and most of this talk is going over my head.
I haven't even read RobA's famous tutorial yet, cos I didn't think I was ready for it. I wanted to get the hang of drawing up a planet before I focussed down to anything like realistic terrain.
Getting basic latitude colour ranges is my first baby step into terrain creation.
I don't have a map I'm working on, I'm just playing with some of the tools to see what they do, so I created a random coast outline. Basically, I'm just trying to add one small step to this:
Rookies Guide to Planets in Gimp
so that all my land isn't plain green from pole to pole.
I don't know anything about Gimp scripts either, but I can snag that one and see if I can figure out what to do with it, thanks.