"How do you feel about calling both tempera and gouache "opaque
watercolor" ? I've seen this at more and more museums/galleries
lately. Your feedback will be appreciated.
Thank you, Deborah Cohen"

It's likely, IMHO, that"opaque watercolor" may be used because it can be
hard to see the difference between tempera and gouache; "opaque
watercolor" is, at least, not untrue.

Carol Morgan