Are you referring to a script within a TXT file or to .c files?
If you mean .c files, Visual Studio Code should automatically detect the syntax and apply the corresponding extension (it asks if you want to download it when you open the file), so perhaps you don't have a C extension loaded.
Visual code open a .C file from openbor game.
If you mean a script within a .TXT file, it's more complex, since you have to define the set of rules (These programs typically assign highlighting rules based on the file extension you open.), and I doubt there's a ready-made extension for that.
I recently started a game from scratch in OpenBOR and created a set of rules for highlighting the entity TXT files, but I use Kate.
