Red key means un-encrypted key. The opposite would be black.

Usually, the key does not need to be exposed. It would be stored in a very hard to break container with some sort of self destruct mechanism. Communication with the box never involve the key itself. And to top it all, the key changes often.

Additionally, protocols usually use the Diffie-Hellman algorithm (or something like it) to generate very short lived secret session keys.

I would go and say (out of my ass) that recent military drones would have 2 or 3 different backup systems for everything, including positionning.

There's a secret key involved in the anti-spoofing part of GPS, but I don't know if it's actually called a "red key" by people who use it.

The wiki article on GPS encryption seems to say that stealing the key for one satellite is possible (720 gigabytes), but the master key at 26 terabytes seems slightly harder to sneak out in an email or USB key. Of course I'm a wiki expert on this, so someone with actual knowledge could probably be more informative.

Those are just the sizes of the pseudorandom sequences produced by a PRNG. They'll be defined by structures much smaller than that. However, that's not the bit that needs stealing, and doesn't even strictly need to be secret.