An accident is a category used for created dependent attributes within the discussion of bodies and substances. It is therefore not applied to God's eternal attributes.
If the mere fact that an attribute belongs to a subject were treated as the complete definition, the category would become too broad. The relevant sort of dependence and the discussion of created attributes must remain in view. Divine knowledge and the color of a body are not two instances of one identical ontological type in this theology.
The distinction is between an attribute associated with a subject in general and a temporally originated accident dependent upon a created substratum.