— Command: invert-face face &optional locale

Swap the foreground and background colors of face face. If the face doesn't specify both foreground and background, then its foreground and background are set to the default background and foreground.

— Function: face-equal face1 face2 &optional domain

This returns t if the faces face1 and face2 will display in the same way. domain is as in face-property-instance.

— Function: face-differs-from-default-p face &optional domain

This returns t if the face face displays differently from the default face. domain is as in face-property-instance.