What does this mean?
One mixer channel has its outline greyed out and some of the buttons and controls don’t work. The pan and fader controls are coloured pale green. I don’t think fader and pan automation are working either.
What does it mean, and how do I get it back to normal?
Most likely: you’ve switched it into “sends” mode, where the fader is now controlling the send level. You have an aux send in the track, and you clicked the “Aux” button on the bus that it sends to. Click it again and it will return to normal.
Thanks - mystery solved.
Yes, there’s aux aux send for reverb.
Actually I got it back to normal by stopping and restarting Ardour, but it’s good to know for next time.