You can change intensity of three basic colors and see what you get by mixing them.

         This procedure shows intensity of each color and resultant color you get by mixing them.

procedure TForm1.ChangeColor(Sender: TObject);
Var
    CRed, CGreen, CBlue : TColor;
begin
    { Display mixture of colors }
    Shape1.Brush.Color:=StrToInt64Def('$'+
    IntToHex(ColorToRGB(Blue),2)+
    IntToHex(ColorToRGB(Green),2)+
    IntToHex(ColorToRGB(Red),2),0);
    { Convert integer to color value }
    CRed:=StrToInt64Def('$0000'+IntToHex(ColorToRGB(Red),2),0);    
    CGreen:=StrToInt64Def('$00'+IntToHex(ColorToRGB(Green),2)+'00',0);
    CBlue:=StrToInt64Def('$'+IntToHex(ColorToRGB(Blue),2)+'0000',0);
    { display circles for each color }
    Image1.Canvas.Brush.Color:=CRed;
    Image1.Canvas.Pen.Color:=CRed;
    Image1.Canvas.Ellipse(X-25, Y-40, X+25, Y+10);
    Image1.Canvas.Brush.Color:=CGreen;
    Image1.Canvas.Pen.Color:=CGreen;
    Image1.Canvas.Ellipse(X-40, Y-15, X+10, Y+35);
    Image1.Canvas.Brush.Color:=CBlue;
    Image1.Canvas.Pen.Color:=CBlue;
    Image1.Canvas.Ellipse(X-10, Y-15, X+40, Y+35);
end;

        When changing track bar position, use following method to change color intensity.

procedure TForm1.RedTrackBarChange(Sender: TObject);
begin
    Red:=RedTrackBar.Position;
    ChangeColor(Self);
end;

procedure TForm1.GreenTrackBarChange(Sender: TObject);
begin
    Green:=GreenTrackBar.Position;
    ChangeColor(Self);
end;

procedure TForm1.BlueTrackBarChange(Sender: TObject);
begin
    Blue:=BlueTrackBar.Position;
    ChangeColor(Self);
end;

 

        This one draws three circles with basic colors at startup.

procedure TForm1.FormCreate(Sender: TObject);
begin
    Red:=255;
    Green:=255;
    Blue:=255;
    X:=Image1.Width Div 2;
    Y:=Image1.Height Div 2;
    Image1.Canvas.Brush.Color:=clRed;
    Image1.Canvas.Pen.Color:=clRed;
    Image1.Canvas.Ellipse(X-25, Y-40, X+25, Y+10);
    Image1.Canvas.Brush.Color:=cllime;
    Image1.Canvas.Pen.Color:=cllime;
    Image1.Canvas.Ellipse(X-40, Y-15, X+10, Y+35);
    Image1.Canvas.Brush.Color:=clBlue;
    Image1.Canvas.Pen.Color:=clBlue;
    Image1.Canvas.Ellipse(X-10, Y-15, X+40, Y+35);
end;

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