I'm no expert either, but, maybe you need an entry in the:
colorBackground[] = { };
something like:
colorBackground[] = {0,0,0,0 };
give it a try.......experiment with the numbers to get different colours.
I think 0, 0, 0........is white.......the final 0 would be the alpha channel setting I imagine.
Edit: It could be that you need this statement within your
Build_center_wall class thingy.
Planck