On the official Sennheiser Germany page I do not find any (color-) variants... There is also only one part number to be found. So I'd guess its either different lighting or retouched... The image by GREQ looks realistic as well, so faking a black version might not be too complicated.
I guess you'll receive the Momentum im brown... and it does look really nice. Only headphone in my small collection that makes me think about what shirt/shoes might fit it if I decide to take it out ;-)