so what happens here is the screen registers the color behind it and recreates it in the best way possible selecting from an existing palette. When you finish drawing, press space to hide and see what the display ended up doing. WARNING: if you want to make the screen display anything, go to object 2 and make your picture up from the palette of colors in one of the costumes, if you don´t use the colors from the palette, a part of the picture may appear purple WARNING 2: if you watch the screen for too long you may get eyestrain
