Huh, greyscale, that's so weird. I had to go check mine just to make sure. I've got two older UT shirts -- Les Toiles du Soleil, which is striped, and a Leo Lionni one -- both all cotton. And the new Lisa Larson one I just ordered says it's 100% cotton:
https://www.uniqlo.com/us/en/w.....var_183000
Oh, I also have a UT tunic-tee with birds on it from some Norwegian design collective, released 2016 -- that one's also all cotton.
Maybe I'm just lucky that my tastes overlap with their all-cotton releases... And yes, the Supima cotton layering tops do usually have about 5% spandex, but I'm okay with it. I wear them pretty form-fitting, as a first layer, so it's nice that the ribbing holds its shape well.
(I do wish the MoMA geometric scarves weren't polyester... that's my biggest gripe this season.)