Alternately many grapes are pretty blueish and almost all are greenish before fully ripe.

Ex: https://www.google.com/search?tbm=isch&q=wine%20grape&tbs=im...

You're all overthinking it. When you are on a boat and you enter deep water in the Aegean, the color does become very dark like thick red wine, different to the blue waters you see from the coast.

I once had a similar discussion about a phrase that was something like "smooth soft stone," describing a surface someone was walking on. It's a straightforward description of a sensation: if you're walking on a stone surface in bare feet, smooth stone feels much softer than rough stone. If you know how it feels, the phrase sounds perfectly smooth and natural, but if you've never experienced it, or don't remember experiencing it as a child, you might think the phrase is meant to sound jarring paradoxical, instead of gently referencing a paradox doesn't even feel paradoxical to us because it agrees with how we perceive the world.

Absolutely. Knowing the phrase "wine dark sea" and its associated discussion, exactly the same struck me when I saw it. Plus reflecting on "verbal" people maybe missing something.