The iMac Pro (5K, Late 2017) "Retina 5K" display, all packed in a thin, dark "Space Gray" housing.
Compared to the "regular" 27-Inch iMac models that this iMac Pro complements, the iMac Pro not only has a dark "Space Gray" housing, but also has a much faster and more advanced architecture and graphics architecture as well as faster memory and storage and additional connectivity, but is much more difficult to upgrade, an unfortunate -- and unnecessary -- limitation for a "professional" system.