GIMP can enable the user to use the Levin matting tool (gegl:matting-levin) which allows for far more accurate feature selection in the Foreground Selection tool. This tool requires that GEGL is compiled with libumfpack. Please add that possibility. https://discuss.pixls.us/t/color-masks-in-gimp/5561/17
I overlooked that this is already possible. Closing.