That same team did the most remarkable (in my eyes) experiment with the same tribe too.

They basically controlled for everything, if you read the paper, except for the language used for colours, and showed how a colour that's incredibly distinct for us, is incredibly hard to distinguish for them and vice-versa.

Go here: https://vimeo.com/120808489 You need to find the odd colour out in the rings at: 5:40 (easy for them, hard for us) 6:30 (so easy for us that it's hard to imagine it being hard for anybody)