The phrase in the original homeric greek is "οίνωψ πόντος". "οίνωψ" is a combination of "οίνος" = wine, and ωψ = "view/look" (related to the modern όψη). So it's not wine-"colored", per se, but it is specified to be "wine-like", specifically in a visual sense. to be fair, this could be other qualities than color, e.g. as others mentioned, perhaps opaqueness.

If it means how "wine appears to the eye", could that also mean how appealing, or repulsive it is?

I don't know or remember what is the context in the original, but for example, a sea that is so calm that it is inviting to travel, or deceptively calm, but if you travel long enough, maybe you will be lost, passing out, going mad or getting destroyed?

I've always wondered if people are misinterpreting wine-dark as wine-colored, when it is the "dark" that is important in description. If wanted to describe dark blue sea, calling it wine-dark to emphasize its darkness would make sense.