Disallow hex colors.
a { color: #333 }
/** ↑
* This hex color */The following patterns are considered problems:
a { color: #000; }a { color: #fff1aa; }a { color: #123456aa; }Hex values that are not valid also cause problems:
a { color: #foobar; }a { color: #0000000000000000; }The following patterns are not considered problems:
a { color: black; }a { color: rgb(0, 0, 0); }a { color: rgba(0, 0, 0, 1); }