In my 25 years of playing, I've never heard of a "red mute". Any ideas? My bandleader said it meant a cup, but later in the song, it had us use plungers while still muted (the notation was pretty explicit), so I don't think cup is the right choice.
The arrangement was from 1942 if that helps.
I found a few candidates on the Intarwebzz.
Here's one possible plunger-ish item,
Overall, though, I suspect this was a Murphy-specific nickname for some mute. It is possible that the intent (based on some alleged history I found somewhere) that the players were playing into such a mute mounted on their stands, and thus adding a plunger mute to the horn itself would allow you to play with both mutes at once.
