the colours and textures are not definitive - they are just something to work with trying to master the technique.
i have project dogwaffle too, but mostly i use zoner draw, xara xtreme, photofiltre, artrage, artweaver and inkscape together with some viewers like irfan view.
i am so glad i am not the only one who has those problems with the gimp, i more or less felt like an idiot that it did not work properly.

"The light at the end of the tunnel may be an oncoming train"