I have, to date, tried my Wii U on three different TVs. Once when I was initially setting it up (using the TV closest to the router so I had 'net access to download all of those updates), once on my own TV/monitor, and once on the TV out on my parents' entertainment center.
Now, my TV/monitor is the only one that's HDMI capable, so I'm using a component/compsite/whatever-it's-called audio/video cable to connect to my parents' TV.
The problem is, every time I turn the Wii U on, the colors are all washed out or even totally grey. This happens every time I turn it on, and they remain washed out until I go into the TV settings--it is set to 480i, and if I try to change that, it detects the TV's capability and automatically sets it... to 480i
I can play fine on that setting, until the next time I have to power the system down; once I turn it on again, I have to start the process all over again.
The other problem seems to have to do with the Wii mode.
Specifically, the picture remains in Wii mode as it was in Wii U mode, meaning I can play games without any difficulty seeing them... until I need to go BACK to Wii U mode. Then I lose the picture on the TV completely; not just washed out, but GONE, until I go into the system settings and make it detect the TV all over again.
*Update*
Correction. I powered on the system this afternoon... and the TV showed no signal at all, not even washed-out/grey, until I went into the console's display settings.