Note :- to use this feature you must have version 1.9.0 or higher of "woocommerce color or image variation swatches" plugin.
To enable this feature visit swatches tab under woocommerce/settings menu and enable checkbox "Enable default attribute options". Upon checking it you will see another table where you can configure your global attribute options. To set colors or images for specific attribute values click on "set color/images" button.
Please remember that this feature will work only for products which does not have display type set. if you have existing products with "custom color or image swatches " as display type then global changes will not affect it but you can always change display type to "global values" in variation select tab to make global values work on those products. "global values" option in display type dropdown will be available only to attributes that are created under product/attribtues not for "Custom product attribute"(which you separate via "|").