Well, if you figure out how to actually make anything conforming with the FST, PLEASE drop me a PM and tell me how.

All the YouTube tuts are for making new creatures and other figures.
And unfortunately, yes, that's what I'm getting with 2.6.8 too. Maybe the manual writers were on crack, or maybe the feature was written out. Or maybe it's one of those things where you only see that if you right click on a Tuesday with the paintbrush tool selected and gradient fill turned on and a color that is some hue of combined green and orange. (GIMP has a fair amount of them.)
Either way, I can't help you.

In the five years I've been using GIMP I have never once had a need for the palette tools, so I never learned to use them.