Programs don't just "die". Something has changed on your machine. I tried to help in my first reply, but you didn't seem interested.Good luck with the problem.
"Programs don't just "die"" Really? How long have you been using computers? I'm in my 37th year of continuous use of computers and software (hardware design, coding, software development teams, hardware development teams, hardware and software support, heavy app user from CAD, automation, network. remote diagnostics, and basic apps). I have encountered endless numbers of cases where "Programs" do indeed, just "die" typically from some sort of "collision" in the code itself that happens in some specific combination of (computer) environmental and use conditions. Also often by the program "glitching out" while it is updating some file the program uses to keep itself "current" like settings, defaults, libraries, setup options... and that glitch corrupts the file so that even if you uninstall the program, that "custom" file gets left behind and when you re-install, the freshly installed version finds the previously "broken" file that happened when the software glitched. If you are doing software support, I should not have to be explaining this to you and you should never have said "Programs don't just die" because, in fact, in the real world programs DO just die... sometimes from their own issues, sometimes from temporary issues within the computer that no longer exist, and occasionally from a "hard," always-present fault in the computer. The latter being the easiest sort of problem to identify and correct (except that nothing remotely like that exists on this computer at this time). This explains why I asked about info for removing every file MC21 might leave behind when I uninstall it. I can find the EASY ones, like the file or files put in my user account, but if the problem can't be coming from a "bad" file left behind in my user account directory because I deleted those after uninstalling MC21... so if there are any other files MC21 would leave anywhere else that could have gotten "whacked" causing a fresh install to read the file and causing the same bad performance issue (no color, sometimes plays video at double speed, etc.).
As for "I tried to help in my first reply, but you didn't seem interested.Good luck with the problem." Let's examine what you are calling "help".
"That's very strange." That's not helpful... sorry, just being honest. If it wasn't a strange problem, I never would have asked about it in the first place.
"It's as if the machine is having severe trouble reading the files." That's not helpful either, I already told you the same files are played fine with other media players and even named some of those that play the same files, from the same NAS drives, with the same driver set with zero problems. So the computer is having ZERO problems reading the files. That should be abundantly clear when apps like Microsoft Movie & TV player from Windows 10, Foobar2000, VLC Media Player, and three more media players all read and play the same files from the same NAS drives without problems. NOTHING is having trouble reading the files. So, sorry, not a helpful reply.
"Antivirus is a possibility." OK, maybe. I ignored that initially because I haven't had anti-virus software interfere with ANY app on a computer since 2004 or so. So I disabled the anti-virus software, re-opened the freshly re-installed MC21 (but without deleting any files MC21 may have created that are not in my user directory since I don't know where to look for them or if there even ARE any files MC21 would leave behind after uninstalling because you keep refusing to tell me. So mark this one potentially helpful, but disabling anti-virus did not change playback so the problem remains.
"There is a thread called Weird Problems in my signature. You might find other ideas there." I had already looked there, before ever posting the question here. Nothing there appeared to apply to my computer or to the problem I'm having."
"You could try restoring an old backup, but I doubt that it will help." Well, this is something, but like you, I doubt it would help either and because I don't seem to be able to get any information about files MC21 may create and store at locations other than the user directory, I'm not sure WHAT to restore from an old backup. I don't want to restore the WHOLE COMPUTER from an an old backup as I would lose things I don't want to lose. It is more efficient to get rid of 100% of files MC21 installs or creates as it is being used and do a fresh install from a state that replicates a computer that never had MC21 installed before. Which is why I keep asking about locations and files I should delete to insure a complete "eradication" of all traces of MC21 to be absolutely certain that one of those files might have a bad sector or three that causes a new MC21 install to behave like the original/previous MC21 install (like the b&w video).
So I'm still back to the question you keep refusing to answer... are there files MC21 creates that are not removed by MC21 uninstall AND that are NOT located in the user directory or the MC21 install directory (in Program Files) and if so, where are they located so I can delete all of them in case one of them happened to have bad data written to it? You keep saying "something changed" -- I don't doubt that, but there nothing in the COMPUTER causing the problem because so many other media players have no problem with the same files. That points STRONGLY to the "change" being in some file that UNINSTALL doesn't remove and some file that's NOT in the user directory because I deleted those after the re-install with no change.