Thank you for using the Support Forum. Please take a look at the solutions for grey background. I know yours is blue but the same solutions apply.
The scanning glass is spotless. The blue tint is a uniform hue across the entire page. A dirty glass would produce streaks.
Maybe those scanners need maintenance/cleaning.
We own a number of the Xerox 3125 documate scanners. They work great. However, some of them are failing with the same issue - they begin scanning images and saving with a light blue background. Color or B&W scans. We have tried on Windows 7 and Windows 10. Complete re-install of scanning software does not cure it. If we move the scanner to a different workstation, the problem follows the scanner. We have had this problem on scanners that are 4+ years old, and a few that are less than a year old. So far, the only solution is to buy a new one. Is this a failure of the scanning lamp?
I should add that the original documents all have a white background.