Автор: http://www.swissdelphicenter.ch

// 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;