It's not clear whether you have a Streaming Stick 4K/4K+ or Express 4K/4K+ (Express 4K = HDR10 max, Streaming Stick 4K = Dolby Vision max)
Regardless of the above your C1's "HDMI Deep Color" setting can ONLY be enabled when the HDMI input is active - you'll need to switch to the Roku's HDMI input and then go to Settings/General/External Devices/HDMI Settings/HDMI Deep Color = 4K
If there is an issue impacting the ability to change the C1's settings with the most recent C1 firmware version you may need to Factory Reset the C1 (or wait of a newer firmware for a fix, if its a known issue).
Try fully powering off the C1 for 3 minutes (unplug from AC) then powering it back on and checking the ability to change settings - if that doesnt address it you may need to do the Factory Reset (its actually best practice after firmware updates, folks rarely do it for obvious reasons).
I have Roku streaming stick 4k. I played with the deep color setting while the stick was inserted in the TV and it was powered. The problem is not that I can't turn the deep color on. The problem is that when I do it, I get black screen with some DV content.
I don't understand your last sentence. If I do a factory reset, that will erase the latest update, wouldn't it? Do you suggest to do a factory reset just to see if that solves the problem? It would be short lived, until the TV decides to do an automatic update. BTW, I turned off the automatic updates on the TV but it still updated to firmware 3.51.15.
Firmware 3.51.16 just become available. I installed it, but I get the same behavior. I really don't want to do a factory reset since I made some fine tunning and it will take me some time to remember how to do it.
