I've got CC, CC2014, CC2015, CC2015.5 and CC2017 and they're all up to date. I've also got two different plugins for JP2 (JPEG2000.8bi and j2k.8bi). No matter which version I try, if I do a plain vanilla Open, the file opens in grayscale, sometimes with a message, sometimes not. If I open it using Open As..., I get the message in my screenshot and then nothing. The mode change business does the trick, although it seems a little convoluted and definitely not intuitive. It's funny, though, that Affinity Photo simply opens it up without any fuss — and no, I'm not pimping for Affinity. The only reason I even thought of opening it in Affinity is because of what I noticed in my file manager: I don't know what that's about. Affinity hasn't stolen any other file associations.
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