The red is FS (and I think actual altitude). The yellow comes from the Snapper screenshot program which gives the aircraft's location and altitude. I'm thinking that it reads off of the altimeter which I probably hadn't reset due to a change in atmospheric pressure enroute. Sloppy pilotage I know, but if I can see the ground, I don't pay much attention to the instruments on approach and landing. Unless I'm in a dive, then I keep one eye on the altimeter like a hawk so that I don't go splat.