GTKD - overrideBackgroundColor of Button doesn't work

[TheDGuy via Digitalmars-d-learn]

Hello,
why does this code not work?

         RGBA rgb = new RGBA(1,0.5,0.5,1.0);
         Button btn_1 = new Button("Start");
         btn_1.overrideBackgroundColor(StateFlags.NORMAL, rgb);

The color of btn_1 just doesn't change.