I come 4 month later....
thanks to have made available your work on this.
I have noticed that, with a totally black alpha layer (and a "hex color"=44, 45, 45):
-the upper left pixel gives the shadow color of the score
-the adjacent pixel immediately on the right is the transparent color. But this color, if present under the score number, will show up through the antialiasing pixels!
illustration :
Here the shadow and the transparent color are the same (red) making the shadow transparent everywhere BUT through the anti-aliasing of the score.