Darken or Lighten TColor?

From :http://www.swissdelphicenter.ch/torry/showcode.php?id=1411

Author: TheB_6030  Homepage: http://nav.to/PenguinProductions/

// Takes a TColor and returns either the lighter or darker color, depending on

// the supplied integer (percentage of original to add or subtract)

// I don't know if this is 100% correct - I did it away from my computer.

function TMainForm.ChangeColor(InputColor: TColor; Lighten: Boolean; n: Extended): TColor;

var

 r,g,b: extended;

begin

 // Grab RGB values

 r := GetRValue(InputColor);

 g := GetGValue(InputColor);

 b := GetBValue(InputColor);

 // Do the operation

 if Lighten = True then

 begin

   r := r+((r/255)*100);

   g := g+((g/255)*100);

   b := b+((b/255)*100);

 end else

 begin

   r := r-((r/255)*100);

   g := g-((g/255)*100);

   b := b-((b/255)*100);

 end;

 // Check whether result is in range

 if r > 255 then r := 255;

 if r < 0 then r := 0;

 if g > 255 then g := 255;

 if g < 0 then g := 0;

 if b > 255 then b := 255;

 if b < 0 then b := 0;

 // Send it out

 Result := RGB(byte(Round(r)),byte(Round(g)),byte(Round(b)));

end;