The phrase that Homer used to describe the sea is typically translated into English as "wine-dark". I don't speak Japanese, but would be curious to know if the author here is translating the phrase from English or the original Greek.
It's actually oinops (oinos = wine + ops = eye/face), which makes no sense in modern languages. The translation wine-red was adopted by interpreters because there are two places in Homer where the word oinops is used directly to refer to color, and both refer to reddish-brown color (and Greek wine IS red). The translation wine-dark is a "solution" made by interpreters who want to make it make sense. However, there are actually many other places in Homer where color weirdness happens.
The most likely explanation is what is given in this manga. The ancient Greeks probably had a looser understanding of the concept of "colors". We have to remember that the idea of colors as we understand it in the modern world was invented arbitrarily by Isaac Newton in his description of light spectra. Ancient people understood "color", "hue", "gradation", and "contrast" as the same thing. It's likely that the original reason oinops is used to describe the sea is because Homer was using the term to describe color, hue, and contrast at the same time and ignored the color part for his description of the sea. We can't do this because of the way our modern conception of color works. This is why the translation wine-dark is most commonly used and is probably the closest to the original intent of the author.
Edit: After looking through this a bit, I found out that the classical Japanese translations of the Iliad and the Odyssey was done by Doi Bansui in the 1940s and he followed the "poetic explanation" given at the time that Homer was making allusions to the sea being violent and bloody. That's why he used "wine-red" in his version.