No trace of gray in the nvidia shield we have tested.
http://imagehosting.biz/images/2019/08/25/6e4abd72-2415-4d28-82c3-6c3b0f55d080.jpg
http://imagehosting.biz/images/2019/08/25/c05686d7-fd9c-44ef-8ecf-afe0685d41b1.jpg
Do you see the loading percentages messages at the bottom, when you launch casting like this:
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http://imagehosting.biz/images/2019/07/05/device-2019-07-05-124945.png