颜色渐变

var
  I:Word;
  Y,YStep:Real;
begin
  Y:=0;//设置Y方向的初始值
  YStep:=ClientHeight/256;//设置步长
  for   I:=255   downto   0   do
  begin
     Canvas.Brush.Color:= $00000000+i*$10100;//改变颜色
      Canvas.FillRect(Rect(0, Round(Y), ClientWidth, Round(Y+YStep)));
     Y:=Y+YStep;
  end;
end;