I hope I can explain this without being confusing. On the old win paintbrush 3.1, it had a great feature which I always wanted to get. Not sure if possible with Gimp 2.10. Win PB 3.1 had an eraser feature that would change one color into another color. Example. let's say you have a checkerboard with all green and all blue squares. using that eraser tool dragging it over the checkerboard ONLY the green squares for example will change to another color you want like red the blue would be untouched. Can that be done with gimp 2.10 or even gimp 2.8? If you still don't get what i mean check out this vid at 1:50 into vid it shows what I am looking for.
https://www.youtube.com/watch?v=qk4WYfq_eVg
https://www.youtube.com/watch?v=qk4WYfq_eVg