After updating to Big Sur my external display colors are wrong

I am connecting my MBP 2017 15'' to a LG 27GL850 display via HDMI. It was almost perfectly fine before the upgrade (only slight issues with waking up, had to reconnect often). Now the colors are off - some issues with brightness or contrast, looks like everything is just not displayed in full color. I have tried changing different settings on the display itself but nothing seems to help.

In the following picture you can see the difference between laptop display (bottom) and external display (top).