Use the Window API functions GetRValue(), GetGValue(), and GetBValue(). Example:

procedure TForm .Button Click(Sender: TObject);
begin
  Form .Canvas.Pen.Color := clRed;
  Memo .Lines.Add('Red := ' +
                  IntToStr(GetRValue(Form .Canvas.Pen.Color)));
  Memo .Lines.Add('Red := ' +
                  IntToStr(GetGValue(Form .Canvas.Pen.Color)));
  Memo .Lines.Add('Blue := ' +
                  IntToStr(GetBValue(Form .Canvas.Pen.Color)));
end;