Draw.FillBox (maxx div 2 - 100, maxy div 2 - 100, maxx div 2 + 100, maxy div 2 + 100, red)
this is for turing 3.1.1 but i think it will wrok on all of them. the cls is to refresh the back color.
this is how to use the box code and colorback
Draw.FillBox ( x1, y1, x2, y2, Color : int )
colorback ( Color : int )