protected function constructRGB($red, $green, $blue)
    {
        if ($red < 0)     $red   = 0;
        if ($red > 255)   $red   = 255;
        if ($green < 0)   $green = 0;
        if ($green > 255) $green = 255;
        if ($blue < 0)    $blue  = 0;
        if ($blue > 255)  $blue  = 255;

        $this->r = $red;
        $this->g = $green;
        $this->b = $blue;
    }