Figured it was LaTeX, but wanted to make sure. So, there are 2 possible fixes for this.
The first is to define quotes properly. That is, using "
renders incorrectly. I'll be honest, I didn't know about that until I came across the following post (link). I think this would be the correct thing to do.
The second method is to modify the tmLanguage file. The following scope is being applied to that string invalid.illegal.string.quoted.double.latex
. You can remove the associated pattern from the tmLanguage file, and it should stop that highlight from occurring. If you want to take this route, let me know and I can provide some additional instructions on how to do it.