I also have seen this but its yellow for me lol. I still have not figured out why this happens either.
We get blue background (instead of gray) on our iGen5s. Both of the machines get this same blue screen covering the entire sheet, usually only on one side. This has been an issue for the past two years. There is no warning, and to get rid of it we usually have to restart the press. Its not an everday thing, just some weird random thing that pops up from time to time. Its not specific to any one paper stock. Anybody else out there in iGen land having similar issues?
I had the same issue racently. its all over the sheet right? just gray everywhere? I replaced the dev house material and that helped but what fixed it was working with my technican to recalibrate the TC senor inside the black housing.
good luck it took a lot of trial to get to where I am.
My background turned gray in the middle of a job I had running to the stacker. I cleaned the MOB sensors, ETAC sensors and Patch Generator then ran color maintenance. Still have the gray background.