Color fillColor = Color.FromArgb(0, 0, 0, 0); //(a, r, g, b)
e.Graphics.FillRectangle(new SolidBrush(fillColor), e.ClipRectangle);
This is actually rather amusing. It means that you are drawing something completely transparent – so this changes absolutely nothing! 🙂
Guess: if black (0,0,0) should mean “glass”, how about drawing (1,1,1) to get (almost) black?