Is This the Ghost of Robin Williams on TIME Magazine's Cover or Just a Printing Error?

A cover of TIME magazine purportedly showing the late Robin Williams as a ghost is being offered on eBay at a starting bid of $10,000.

The ghostly copy was mailed Periodicals class to a U.S. address. The design is exactly the same as a regular cover except what is black on the regular cover is gray on the haunted cover.

I'm calling on my fellow printing geeks for an explanation, but I'd say it was a simple case of the black ink missing.