Pixel 4 XL in unreleased gray color option shown off in photos

The Pixel 4 XL is available in three color options, but a new leak has revealed that Google may have considered a fourth color during the phone's development.
A gray Pixel 4 XL has appeared on Chinese marketplace Taobao (via XDA-Developers ). The back of the phone has a dark gray paint job with a lighter gray on the power button, both of which are different from the three colors that the Pixel 4 and 4 XL launched with: Oh So Orange, Just Black, and Clearly White.
The device is covered in warning stickers and barcodes, including some that seem to identify it as a Verizon model. We can also see that this device is an EVT, or Engineering Validation Test, prototype. 
Another sticker on the back of this Pixel 4 XL warns that it "has not been authorized as required by the rules of the Federal Communications Commission and Industry Canada, nor has it been tested for compliance with EU regulations." The device is only meant for "internal testing and development", and around front is another sticker that warns that it shouldn't be removed "unless authorized by hwpasafety@".

This particular Pixel 4 XL features 6GB of RAM and 64GB of storage, and the seller is asking 2699 yuan ($382 USD) for it.
It's unclear if this gray color is one that Google actually thought about releasing to the public or if it was just meant for this prototype. Whatever the case, it's a nice-looking color that offers something a bit different than the black and white paint jobs that we see on a lot of smartphones but also isn't a super bright 

Google Pixel 4 XL