I havent; tried this with hammertone but it works with wrinlkle paint.
with wrinkle paint I just spray it with wrinkle paint, black is the most common , then spray over that after it’s dry and wrinkled with the color of choice.
hammertone has a slightly bumpy surface so maybe you could try applying that and then follow after dry with a metallic paint, You might find the metallic particles lay a bit more random because of the bumpy surface underneath ? it would be an experiment?
I went to lordco autobody several years ago and asked for a certain color and the paint guy handed me a book of swatches, each had a different year of car and I found the best match that way. It was for a crosley D-25 in the blue grey metallic color.