It looks like this problem has been well-known for a few years now, but no firmware fix from Roku to keep from trying to Dolby Vision transcode rec 709 material in MKV containers when being sent to 1080p display devices.
I reached out to online chat and phone support yesterday, but spent two hours having people tell me to reset my Roku and try again - beyond worthless.
It appears OS 13 has finally solved this issue. Can you verify?
No, it doesn't appear fixed. If I force direct stream on my Plex client, the color is interpreted wrong on the Roku. If I let Plex transcode (which my NAS is not fast enough to do reliably for a 4k stream), it displays the correct color.
Obviously my preference at home, and for almost all of my viewing, is to direct stream rather than be forced to transcode to see correct colors.
Just a note confirming that the bug still exists in the 4850x (Roku Ultra 2024). I'm sending it back.