Mojave - Washed out colours

Hi all,

Having some issues with colours after installing Mojave on my Optiplex 790 (i5 2500, Quadro K600 GPU with WhateverGreen) where some scenes are washed out/too bright (noticed firstly in Safari/Chrome), especially compared to the same sites on my rMacBook Pro (connected to the same model monitor beside the HT monitor). On both machines the HD 709-A profile is selected. Both are connected via HDMI (DVI>HDMI on the HT, HDMI-out on MBP). The Mojave wallpaper looks noticeably darker also.

Any ideas on fixing this? Is there anything I can copy over from my MBP? Read something about DisplayMergeNub but am not sure if that'll work here?

Thanks in advance!