I changed Folder Colour today, for fun, to see what it does, and I had 2 folders open and it changed it to Red on the one I wasn't on. Strange. I then go to Folder Colour again (by right click context menu) to change it back to Yellow. It basically doesn't let me know since it thinks I'm on Yellow, in both of the folders. I closed the folder, re-opened, it opened Red. I then try to open it and change the colour to orange, but it seems it reverted back to normal. I open Folder Colour again and it is on orange. I change it to yellow and it allowed me. However, there was no colour change, both looked the same as default yellow.
Right click anywhere where there's whitespace when viewing files and click Folder Colour.
Or, I just tried now, right click on a folder and change its colour. It bugs out and doesn't let me change back to Yellow.
It also doesn't refresh quickly the tab bar folder color, or at all actually, until I get out of the folder and go back in.
Edit: It let me change it back but it takes time for it to allow me. Basically, I have to leave it alone and come back to it later.
Oh my goodness, very sorry. It seems to be a new OneDrive feature. I never knew since I never used it and I thought it was only DOpus feature lol. My apologies!