CSSmin::compress_hex_colors PHP Method

    private function compress_hex_colors($css)
    {
        // Look for hex colors inside { ... } (to avoid IDs) and which don't have a =, or a " in front of them (to avoid filters)
        $pattern = '/(\\=\\s*?["\']?)?#([0-9a-f])([0-9a-f])([0-9a-f])([0-9a-f])([0-9a-f])([0-9a-f])(\\}|[^0-9a-f{][^{]*?\\})/iS';
        $_index = $index = $last_index = $offset = 0;
        $sb = array();
        // See: http://ajaxmin.codeplex.com/wikipage?title=CSS%20Colors
        $short_safe = array('#808080' => 'gray', '#008000' => 'green', '#800000' => 'maroon', '#000080' => 'navy', '#808000' => 'olive', '#ffa500' => 'orange', '#800080' => 'purple', '#c0c0c0' => 'silver', '#008080' => 'teal', '#f00' => 'red');
        while (preg_match($pattern, $css, $m, 0, $offset)) {
            $index = $this->index_of($css, $m[0], $offset);
            $last_index = $index + strlen($m[0]);
            $is_filter = $m[1] !== null && $m[1] !== '';
            $sb[] = $this->str_slice($css, $_index, $index);
            if ($is_filter) {
                // Restore, maintain case, otherwise filter will break
                $sb[] = $m[1] . '#' . $m[2] . $m[3] . $m[4] . $m[5] . $m[6] . $m[7];
            } else {
                if (strtolower($m[2]) == strtolower($m[3]) && strtolower($m[4]) == strtolower($m[5]) && strtolower($m[6]) == strtolower($m[7])) {
                    // Compress.
                    $hex = '#' . strtolower($m[3] . $m[5] . $m[7]);
                } else {
                    // Non compressible color, restore but lower case.
                    $hex = '#' . strtolower($m[2] . $m[3] . $m[4] . $m[5] . $m[6] . $m[7]);
                }
                // replace Hex colors to short safe color names
                $sb[] = array_key_exists($hex, $short_safe) ? $short_safe[$hex] : $hex;
            }
            $_index = $offset = $last_index - strlen($m[8]);
        }
        $sb[] = $this->str_slice($css, $_index);
        return implode('', $sb);
    }