This saved my tablet, thanks. I managed to use fastboot from Windows 10 but it did not work the first time. After I rebooted and changed USB port, fastboot was actually working with my tablet, and I could follow the instructions.
I had the same problem, and this is a setting in the TV related to HDMI. It's called full RGB, that was not set by default on my TV. On Google, search HDMI full RGB vs Limited (I can't post a link yet)