$re = '/color:\s*+(?!(?:transparent|inherit)(?:;|$))[^@;\n][^;\n]*;?/m';
$str = 'I want to capture all colors that are not "transparent", "inherit" or starts with an "@" character.
should be captured
--------------------------
color: blue;
color:red3434;
color: red3434;
color: #00FF00;
color: #F0F;
color: face(@B23);
should not be captured
--------------------------
color: transparent;
color:@transparent;
color: @transparent;
color:inherit;
color: @B23;';
preg_match_all($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