See, I like simple icons, and very often I only add complications because they're made for an icontest. But... getting a really pretty simple icon is very rarely merely a case of cut+paste, and I've often spent a long time on a colouring that someone who hasn't seen the source pic would never realise is anything different. (Which is why I'm intending to put the source photo up with the voting on severalplums.

I can't help you with GIMP, as I've only ever used Photoshop - but I expect there is a GIMP tutorial community around somewhere, which might be useful. For some people, it helps to find out that things like Layers exist (I did not know about layer blend modes when I started making icons), but I know you are somewhat more informed than that!