Looks like the displays
are exactly the same, but the 850 has
additional "Super Resolution+" & "True Color Pro" LG software.
I'd start by trying 1 or 2 things. Either remove/disable the True Color software on the 850 and punch in some numbers manually on both monitors (
something like this). Or see if you might be able to install the True Color
software for
both monitors. I have more faith in the first idea, but you never know.
If those fail you may need some sort of hardware
solution.