Place the machine up for service. The IIT pwb with new NVM must be replaced for this exact background issue
First of all, the optical system must be well cleaned, the system software to be up to date, and if still not work the IIT PWB to be replaced (failure of this board is a known issue on this machine).
I have a Xerox workcentre 7220, a couple of months ago start the problem to make digital doc. in pdf, jpg format, all docs have a blue tone(see pic below) in any quality or size.
The tehcnician argued that the diffuser change was necessary, but unfortunately the problem was not solved and never answered.
I hope you can help me