Put this code in Forms OnPaint event:
procedure TForm1.FormPaint(Sender: TObject); var Row, Ht: Word; begin Ht:=(ClientHeight+255) div 256; for Row:=0 to 255 do with Canvas do begin Brush.Color:=RGB(Row,0,0); FillRect(Rect(0,Row*Ht,ClientWidth,(Row+1)*Ht)); end; end;