im ussing black windows theme for windows so i wanted to have black theme for gimp and no such thing existed so i just
made modification of gimp theme green heart which is modification of blue heart theme for gimp
place extracted FOLDER to \GIMP Portable\App\gimp\share\gimp\2.0\themes
than just start Gimp hit edit>preferences>themes and choose Zero Gimp
after changing theme restart Gimp or the font will be black (after restart it will be white and visible)
here is download link
DOWNLOAD ZERO GIMP NOT GIMP PORATBLE !!!!
and here are some screens