Alpha Index 255 glitch

// http://puzzlum.net/Roe_Web_Builder/mk11TILES.php

<?php

function combotoc($path = 'bsaves/out' )
{
    $nen=nen_ini();
    $return = '';

    $toc = fasttoc( $path, array( '.png' ) );

    $toc_index = 0;
    while($toc_index < count( $toc ))
    {
        $toc[ $toc_index ] = str_replace( '.png', '', $toc[ $toc_index ] );

        $toc[ $toc_index ] = substr($toc[ $toc_index ], 0, strlen( $toc[ $toc_index ] ) - 4 );

        $return.= '<tr><td><h3>'. htmlentities( $toc[ $toc_index ] ). '</h3></td><td style="background-color:springgreen;">'. combo( $toc[ $toc_index ], 127 ). '</td></tr>';

        if( $toc_index < count( $toc ) - 1 )
        {
            $toc_index++;
        }
        else
        {
            break;
        }
    }
    return '<table>'.$return.'</table>';
}

function combo($filename='dtbykick', $alpha = 127 )
{
    $nen = nen_ini();
    $vga = vga_ini();
    $return = '';

    $return.= '<img src="./bsaves/out/'. $filename. '.24x.png">';

    $image[ 'rgb' ] = imagecreatefrompng( $nen['root']. 'bsaves/out/'. $filename. '.24x.png' );

    $return.= '<img src="./bsaves/out/'. $filename. '.24y.png">';

    $image[ 'mask' ] = imagecreatefrompng(  $nen['root']. 'bsaves/out/'. $filename. '.24y.png' );

    $image [ 'combo' ] = imagecreatetruecolor( imagesx( $image[ 'rgb' ] ), imagesy( $image[ 'rgb' ] ) );

    imagetruecolortopalette( $image[ 'combo' ], false, 255 );
    imagealphablending( $image[ 'combo' ], false );
    imagesavealpha( $image[ 'combo' ], false );
    for( $color = 0; $color < 256; $color++ )
    {
        $vga[ 'color' ][ $color ] = imagecolorallocate(
        $image[ 'combo' ],
        ( $vga[ 'table' ][ $color ] >> 16 ) & 0xFF,
        ( $vga[ 'table' ][ $color ] >> 8 ) & 0xFF,
        ( $vga[ 'table' ][ $color ] >> 0 ) & 0xFF
        );
    }

    $vga[ 'color' ][ 255 ] = imagecolorallocatealpha(
    $image[ 'combo' ],
    ( $vga[ 'table' ][ 255 ] >> 16 ) & 0xFF,
    ( $vga[ 'table' ][ 255 ] >> 8 ) & 0xFF,
    ( $vga[ 'table' ][ 255 ] >> 0 ) & 0xFF,
    127
    );

    imagefill( $image[ 'combo' ], 0, 0, $vga[ 'color' ][ 255 ] );

    $width = imagesx( $image[ 'combo' ] );
    $height = imagesy( $image[ 'combo' ] );

    //loop through width and height of source image
    $row=0;
    while( $row < $height )
    {
        $col=0;
        while( $col < $width )
        {

            //get color in image $image[ 'mask' ] at pixel ($col, $row)

            $pix[ 'mask' ] = imagecolorat( $image[ 'mask' ], $col, $row );

            //get color in image $image[ 'rgb' ] at pixel ($col, $row)

            $pix[ 'rgb' ] = imagecolorat( $image[ 'rgb' ], $col, $row );

            //if pixel in $image['mask'] at ($cow, $row) is white:

            if ( $pix[ 'mask' ] === $vga[ 'color' ][ 15 ] )
            {
                //set pixel based on Mask layer's ($col, $row) as fully transparent
                $pix[ 'combo' ] = $vga[ 'color' ][ 255 ];
            }
            //else
            else
            {
                //set pixel based on RGB layer's ($col, $row) with full opacity
                $pix[ 'combo' ] = $pix[ 'rgb' ];
            }

            //assign pixel data to $image['combo'] at ($col , $row)
            imagesetpixel( $image[ 'combo' ], $col, $row, ( $pix[ 'combo' ] % 256 ) + 1 );

            if( $col === $width - 1 )
            {
                break;
            }
            $col++;
        }
        if( $row === $height - 1 )
        {
            break;
        }
        $row++;
    }

    //save resulting image as new file
    imagepng( $image[ 'combo' ], $nen['root']. 'bsaves/combo/'. $filename. '.png' );

    $return.= '<img src="./bsaves/combo/'. $filename. '.png">';

    return $return;
}

function alphaColor($hexColor,$alpha)
{
        return bindec(decbin($alpha).decbin(hexdec($hexColor)));
}

?>