$re = '/(?<!^)<[^>]*>(?!$)/m';
$str = '<color=yellow>Hello <color=cyan>World!</color></color>
<color=yellow>Hello my <color=cyan>name</color> is <color=gray>Kite <color=white>Watson!</color></color></color>';
$subst = "";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
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