This one has four-color gradient.

Download this example

Following procedure create gradient at startup.

procedure TForm1.FormCreate(Sender: TObject);
Var
     C, R, H, W, L : Integer;
     Step : Real;
begin
     { Get form size }
     H:=Image1.Height;
     W:=Image1.Width;

     { Set fill size }
     L:=W Div 3;

     { Set fill step size }
     Step:=255/L;

     C:=0;
     For R:=0 To W Do
     Begin
     { Select color for gradient starting from RED
     to YELLOW }

          { Change fill color }
          If R<=L Then
          Begin
               C:=Round(R*Step);
               { Red -> Green }
               Image1.Canvas.Pen.Color:=RGB(255-C,C,0)
          End
          Else If R<=2*L Then
          Begin
               C:=Round((R-L)*Step);
               { Green -> Blue }
               Image1.Canvas.Pen.Color:=RGB(0,255-C,C)
          End
            Else If R<=3*L Then
          Begin
               C:=Round((R-2*L)*Step);
               { Blue -> Yellow }
               Image1.Canvas.Pen.Color:=RGB(C,C,255-C);
          End;

          { Fill area by drawing lines }
          Image1.Canvas.MoveTo(R,0);
          Image1.Canvas.LineTo(R,H);
     End;
end;

DOWNLOAD this example

Click here to download this complete example for Delphi 6. (File size 4KB)