Oh right, I didn't even consider that it was possible to use a different texture than the other coast tiles. In that case I like that Atolls have lighter water inside them, seems realistic. But you would need to custom build it for the specific tile and orientation, which seems like a bad solution to me. I don't see a downside to have two different terrains for Lagoons and Atolls considering they are quite different. This also serves to enlarge central North America (aka real America) at the expense of the eastern seaboard, which seems like the wrong priority.