$re = '/color+=([\#]{1}|[\w\W]{1}|[\#A-Za-z0-9]{7,})/i';
$str = 'test[color=#663300]test[/color]vdfvd
test[color=#663300]test[/color]vdfvd
[color=#]test[/color]
[color=#]test[/color]
test
[color=#66330gdgf0]test[/color]
[color=#66330gdgf0]test[/color]
test
[color=]test[/color]
[color=]test[/color]
test
test
test';
preg_match_all($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