Before we go any further, did you, by any chance, turn on drive encryption for your drive?
I know that Windows routinely uses blue instead of black for the lettering for files/folders on which you've turned on Windows file compression. Green has been the color for encrypted files for some time now (see these DuckDuckGo search results).
I would be highly disinclined to switch the color back to black, even if it were possible, just because that vital piece of information is then lost. You might be OK if you can choose something other than green, but I'd make it something that you can read but that makes it obvious that this is not likely a plain jane file, but an encrypted one. I can find nothing obvious that would allow this change, but it is almost certainly controlled via the registry and someone may know a hack to allow you to change the displayed color of the text. I do not.
Brian AKA Bri the Tech Guy (website in my user profile) - Windows 10 Home, 64-Bit, Version 1803, Build 17134
. . . the presumption of innocence, while essential in the legal realm, does not mean the elimination of common sense outside it. The willing suspension of disbelief has its limits, or should.
~ Ruth Marcus, November 10, 2017, in Washington Post article, Bannon is right: It’s no coincidence The Post broke the Moore story