if you are just doing squares, rectangles etc then check out the BOX command.
e.g.
box 100,100,400,400, rgb(255,0,0),rgb(0,255,0),rgb(0,0,255),rgb(255,255,255)
note that this will do a gradient fill, with red, green, blue and white in the corners. If you want a single colour just set all of the color values the same
if you are doing complex shapes, do a forum search for 'flood fill'. there are a couple of decent examples from some of he forum geniuses (genii?) that will fill n-gon shapes
This is not the Sig you are looking for....