imagefilter不会完全覆盖边缘

I've got a black logo, that's being colored using the following code

/**
 * Adds the logo to the image, and colours it if the colour isnt black
 */

public function addLogo($color = 'FFFFFF'){

    // Future note: The logo has to be black to have it's colour changed. White logo's don't work.
    $logoImage = imagecreatefrompng(APPLICATION_PATH . '/../public_html/images/widget/overlay/JSLogo2.png');

    // If a hex is passed, and it's not black, colour the logo.
    if($color != null && $color != '000000'){
        imagefilter($logoImage, IMG_FILTER_COLORIZE, hexdec('0x' . $color{0} . $color{1}), hexdec('0x' . $color{2} . $color{3}), hexdec('0x' . $color{4} . $color{5}));
    }

    // Get the offset.
    $offset = $this->getPadding() + $this->_circleWidth + (5 * $this->_scaleFactor);

    imagecopyresampled(
        $this->getImage(), 
        $logoImage, 
        $offset, 
        ($this->_scaleFactor * $this->_padding), 
        0, 
        0, 
        $this->_logoWidth, 
        $this->_logoHeight, 
        $this->_oriLogoWidth, 
        $this->_oriLogoHeight
    );

    imagedestroy($logoImage);

    return $this;
}

The output colours most of the image, but leaves the edges. Is there anyway I can improved the coverage of the colour, or is this the best that PHP will be able to do? Below is a screenshot of the output. The same effect happens on any logo colour and background colour.