I have found the material to feel different (stiffer) on the black vs. the grey. The black stretches less in my opinion. But I didn't notice any sizing differences.
Sidebar- the Loopwheel is definitely much heavier than the regular Escobars. Coming in clutch for this NYC winter.
That's due to the difference in material composition. The black are 100% cotton and the grey are 83% cotton, 17% polyester. The polyester gives it a slightly softer feel.