For the untrained eye, it's easily to mistake one for the other. But when you see both of them side by side, it becomes as clear as night and day. Gris T comes with black resin edging whereas Etoupe comes with the classic brown resin edging. This should be the first clue when deciphering which is which. I personally prefer Gris T to Etoupe.
Both are great neutrals. Etoupe, by far, is easier to come by.
I LOVE both - though a little more partial to Etoupe. Both are in the gray family - etoupe is more brown gray and Gris lighter gray (with more white). And depending on the skin, the colour intensity differs (colours appear deeper in Clemence).
I may be shot down in flames for my opinion here but Gris T works much better as a colour for smart wear. Etoupe in the wrong lighting conditions looks like a white handbag that has got terribly dirty. Gris T always looks elegant. Both would work for informal occasions but Gris T would easily move up the scale in formality depending on what you wear and the occasion whereas you'd have to be more careful with leather type, slouchiness and stitching to achieve the same effect with Etoupe.
I love both but etoupe looked very blah on me. I haven't been able to try on anything in GT to compare. When the search function was working, I found a photo of two Birkins, one in each color, side by side. I believe it belonged to Flossy Figaro. They're both wonderful neutrals. My concern with GT was that it was lighter and would show more dirt and wear. But the enablers here eased my fears. Now I just need to find the bag.