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