I tried to change color classes from the IPTC Info panel and in certain cases I could not change the color class to red (I didn't really try it with other color).
I was captioning photos and wanted to mark red all photos I've set the caption to final state so I tried to set it below the small preview of the IPTC info dialog then I pressed save and move to next. But the color class was not changed. Not just upon the change action but the save did not save it to the photo either.
I had no time to further document the error I will try it tonight if I will have time for that.