The integration cannot create new attributes for drop downs in Woocommerce. So if you create a gridded item with a new option name eg. color, this must be created in the back end of Woocommerce first and added to the integration's attribute map.
If you have only "size" defined as an attribute in Woocommerce, and "color" does not exist, there is no place for the integrator to put the color values. the new attribute will need to be created and the xml value will need to be mapped.
The default for the integration adding new products, ( or new variations to existing products ) is to add with the attributes in the order of 1. color , 2.size.
So if you have a product that only had size and then later you want to add the color attribute, you have to make sure that the Color attribute is set as the first attribute and Size moves to the second or mapping will be switched for any added variations.
Please see screen caps for this instruction on how to add an attribute.