Some good points. Shades of blue would certainly work for an ocean faring Civ.
While all this sounds reasonable though, I don’t think they are going to leave South America with only one Civ through the first expansion pack.
Yeah, it doesn't seem likely that South America won't be getting a civ this time. But that being said, really studying the picture, his nose also seems to look more Polynesian than Native American. Perhaps he could have a nose like that if he is from the far south of the Americas, like Chile and Argentina, so the Mapuche idea is still on the table here, but I would lean more towards Polynesian because of his nose.
And yeah, to me that headband looks kinda fuzzy, which would fit well with a Polynesian style headband, rather than a material headband typically used by South American native peoples.
This one is yellow, but as you can see, Polynesian leaders did wear such things...
I'm also trying to work out what he is wearing, as we get a glimpse of it. It's not much to go on...Could be a cape, which would work well for the Mapuche idea, but that would not rule out Polynesia either.