These bumper cases, like most smartphone cases, are designed to protect the Surface Duo from falls or impacts but are specially constructed to fit the Duo without affecting its foldable dual-screen functionality.
The four colors available are Glacier, Ice Blue, Ember, and Graphite.
Here’s the official Microsoft Store description. Orders can be placed here.
Added protection for your device, this sleek silicone bumper is specifically designed for Surface Duo and the 360° hinge. It adheres to the edge of Surface Duo and supports full mobility of the hinge, while allowing easy access to all controls and the USB-C port, fingerprint reader, and SIM tray. Available in Glacier, Ice Blue, Ember, and Graphite.