$re = '/background-color:\s(?:"(.+)"|(?!url)(\w+)|url\(.+\) (.+?)\s)/';
$str = 'background: "green"
background: url("big_green.png")
background: green url("big_green") no-repat
background: url("big_green") green no-repeat
background-color: "#fff"
';
preg_match_all($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