My color choices have become a large, unorganized mess. I want to organize the choices - "pant colors", "shirt colors", "sock colors", etc. When I add this product attribute, however, I cannot get these choices to come up as a filter item in my configurable products. I see from the attribute grid that these attributes are marked "no" in the "use in layered navigation" field. But, I cannot get that field changed. How do I create multiple color attributes?