Onyx Boox Tab Ultra C seems to be the best color device at the moment, but it is NOT waterproof:
https://www.youtube.com/watch?v=kWq0njylqts
I'm all intrigued by the Mobiscribe Wave Color, but it has the previous gen of color screen instead of the newest one (Kaleido Plus instead of Kaleido 3), so I honestly don't know.
I'm coming from a Kobo Aura H2O, and similar to you, I wouldn't want to lose screen clarity or water resistance. Yet, I see reviewers who make comments like "why would this be waterproof?" SMH. It's very challenging to get any good sense of how good or bad these devices actually are when you can't see them in person.