The issue is not blinding the poor farker behind you on a clear day. You can have the red lens with no prob whatsoever. The only time it will become a problem is if in fact it is switched on and there's no fog.
In your case, being that its just a lens, you don't even have the option to turn it on, and it will only be on when you engage reverse, therefore it won't ever be a "fog" light, so you can never get done for it :-)
Unless your one of those folk who drive backwards!!