If the OPTION element's VALUE attribute is specified you might use an attribute selector, like this:
CODE
option[value="-1"] {color: red;}
<select>
<option value="1">foo</option>
<option value="0">bar</option>
<option value="-1">baz</option>
</select>
If the VALUE attribute is not specified (a value can be specified with the OPTION's content as well) the above won't work, though.