Try setting the screen bit depth as well,... or try it in a window.
graphics3d 1024,768,0,2 ;choose bit depth, run in a window
graphics3d 1024,768,16,1 ;run in 16 bit mode, fullscreen
graphics3d 1024,768,0,2 ;choose bit depth, run in a window
graphics3d 1024,768,16,1 ;run in 16 bit mode, fullscreen