This was not added to the usfm.sty file that comes with Paratext. I’m guessing that someone on one of the teams that you “share” with made the change and then did a S/R which propagated the corrupted file. This can be difficult to fix once it is out in the wild.
You should S/R a clean copy of the file and make sure that everyone on the team receives it.
If someone wants to add color to a marker they should use the custom.sty file. Help provides information on how to create a custom.sty file.