In CSS, valid color values actually fall into three categories: RGB (or RGBA) values, hexadecimal values and named color values (such as red). The CSS specifications don't allow for the use of named color values other than those listed in the aforementioned page. All other named color values, such as yellowgreen or darkred are considered invalid. Here are the validation results obtained from trying to use one of these invalid color names.
As you can see, these kind of values are invalid CSS.