GTKD drawing area remains white even SourceRgb is changed

[TheDGuy via Digitalmars-d-learn]

My code:

http://dpaste.com/1X3E1HW

i store colors in the accumulator-array and draw them via 
"cr.rectangle()". Because i have some problems with the code i 
set the SourceRgb-color to a constant value but if i execute the 
program, the window remains white.