i'd say definetly keep a close eye on them the next couple of nights without the use of the red light. If it happens to be peaceful now without the use of the red light then it's most obviously the red light causing some kind of reaction in your JD
Wasn't watching this thread til pm received...
I have noticed with many fishes that they are extremely agitated and respond by either threat posturing or actually attacking when the operculum are flared and the gills made patially visible... the red gills as you well know. But I've also noticed something related and my "won't eat any dither fish" male JD is the one that does this...
I don't have thermometers on my tanks. They can't get warmer than the room most of the time anyway, but neither here nor there.
To check temp, I hit the surface and bottom front glass with a handheld IR thermometer. Its quick and easy and accurate. However, I misplaced the IR one day (left it in the car) so I switched to my slow but accurate backup... those floating glass thermometers with the little steel beads sealed in wax at the one end... RED WAX!!
My JD was attacking it before I ever got it in the water, and he wouldn't stop either.
It would seem red light is to territorial fish as the matador's cape is to the bull, but like the bulls, not all respond "favorably" and attack it.
My female EB couldn't care less about the old thermometer... my wild type female is another matter. She also attacks the red wax area.
Just some observations for pond

ering.
It would seem that the only light available to reflect off any fish in a red light only environment... is red... territorial fishes quite possibly perceiving this red displayed from their tankmates as a posturing, and responding accordingly.