I have an issue with the Wii U, where blacks are rendered as grey about 80% of the time I turn it on. The image is what you'd normally get when you send a limited RGB signal to a display expecting a full RGB signal.
This issue only occurs when routing the Wii U through a receiver's HDMI switch. I've reproduced this issue with Denon, Marantz and Pioneer receivers feeding Sony and Samsung televisions. Onkyo and Sony receivers didn't have this issue. Switching inputs on the receiver or TV and then switching back to the Wii U acts as a workaround for this issue, restoring the proper image.
I've talked in detail with support from both Denon and Sony regarding this issue and they both point their finger at the Wii U. I'd like to know if anyone else has noticed this and whether this is something we can expect to be fixed in a future firmware update (hopefully the fall update).
EDIT:
I should add that all TVs used for testing support both limited and full range RGB signals.