$re = '/(?:color:\s*|pid=\d*)#(*SKIP)(*F)|#(\w+)/m';
$str = '<span style="font-weight: bold;">test1<span style="color: #FFA500;">test2</span>test3</span>#hello#how#are#you
<span style="font-weight: bold;">test1<span style="color: #FFA500;">test2</span>test3</span>#lalala #hello
<div class="post_body" id="pid_58705">
<blockquote><cite><span> (Hoy 02:42)</span>Moroha escribió: <a class="quick_jump" href="http://test.com/Thread-hello?pid=58672#pid58672" rel="nofollow"> </a></cite>testing</blockquote></div>
pid=97589735935795358672#foobar';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php