In the refueling mission, and others that I haven't enumerated, the Flight menu is black, no matter the frequency I use. I'm using the simple modelling, which switches to the correct frequency for ATC/Tanker, even when I specifically change to frequencies that are incorrect, so that those choices are black. I've seen reports of this from the past and a fix was apparently to re-save the mission. I've tried that to no avail.
In a separate AG mission I noticed the same behaviour but changed the starting frequency to the channel of my flight, instead of switching the freq in-sim, and I could communicate. In the refueling mission, though, there is no mention of the flight frequency, so maybe it was never set up? I'm not sure what to expect with single player missions, as far as completeness of flight comms.