I read the thread about HDR10+ on Roku TVs. I have the 43" and 50" Select Series TVs, and no matter what expert settings and combinations I try, HDR10+ on both TVs looks washed out and the colors dim. It's almost like watching 1960s TV. I was able to access the "secret menu" and like others frustrated with HDR10+ on newer Roku TVs, there is no option to turn it on and off. My TVs are new.
I was able to improve my problem by hooking up a 4K Ultra HD Roku streamer box to the TV. It had been used on a Vizio TV that died (replaced by a Roku TV).
I changed the Roku TV audio setting to Auto and paired a spare Roku remote to the streaming box (not to the TV). This gave me access to the menu and all my Roku channels loaded after activating the box as a new device.
Note: turn "1 touch play" CEC off on the streambox and ON for the TV so you can switch back and forth with remotes. Just select the Roku streambar box as an Input through the TV to switch to it. Click the Home button on the Roku TV remote to exit the box and return to the tv.
Go into the Display Type menu of the Roku stream box. The default is 4K HDR10+. I changed it to 4K Dolby Vision HDR TV. Tried it out anyway and it worked. Now go to the programming you want to watch. This may or may not work for anyone else, but for me, the picture is sharper, clearer, and the colors more vibrant.
It's inconvenient to use 2 separate Roku remotes (1 for HDR content through the stream box, 1 to watch the native Roku TV) but it beats the alternative, at least for me.
Roku, please listen to your fans and customers: do a firmware update to your Roku TV Select Series so that users can turn HDR 10+ on and off in settings rather than resorting to extremes. Thank you.
