are you sure this leads to a color that makes the white letter readable you need to do something on drawfallbackiconletter to draw either white or black depending on the luminosity of the background  based on w c recommendations  here is what you do def luminance r  g  b for each c in r g b c c if c then c c else c c l r g b return l l luminance r  g  b if l use else use  f that s the way to go  there s already a getrelativeluminance that you could use instead  but it is garbage  