"They see the green oceans."

Translation: Kastra embrī urnesi.

[frpmacc]

So is kastra/kastor green or blue?
Or is it like Japanese 青い that is usually blue but in some contexts green? If so, in which contexts is it which?

[StephieRice]

It is both. More accurately green and blue are not distinguished in the same way as English. This is a common thing amongst other languages as well, color itself is an absolutely arbitrary thing that is completely hallucinated within our mind. It is up to us to create labels and to distinguish them from one another although there are arguably 3 colors that are distinguished at our retina.

Edit: for this language, and I might be 100% off base here, I think of "kastor" as "sea-colored"

[Dedalvs]

It's not exactly like Japanese, but that's a good analog. See StephieRice's comment below.