You can find this filter through
-> -> -> .
Adjust FG-BG belongs to color map filters which
make connection between a color source and an image. Here, image pixels
having ForeGround color will turn to black while pixels having
BackGround color will turn to white. Other colors will turn to their
complementary color. There will be no change if FG is black and BG is
From left to right: original image, after applying Adjust FG BG