Chosen Solution
after upgrading a customers iMac from Mojave to Catalina there is this blue hue bar under any white window. I dont think the upgrade had anything to do with it, its just thats all i have actually done with it since i have had it in our workshop. Update (01/31/2020) it looks like a panel fault. but find it strange its only become visible after an OSX upgrade. the blue hue bar moves and follows the window , its not a static issue.
This series uses LVDS signaling between the LCD panel and the logic board. Unlike iDP (eDP) signaling, LVDS is sensitive to signal disruption. Does it look like the system was opened at some point? It’s likely has a damaged cable or has some liquid damage on the connections where the signal is leaking to the ground lines via corrosion.
