macOS may show colour banding on an external display. To solve the issue, we need to follow the steps:
- Download the ZIP package of patch-edid.rb and uncompress it
- Type in ruby in Terminal and drag patch-edid.rb so it will look like ruby /<path>/patch-edid.rb, and then press the return key
- You will find the folder DisplayVendorID-xxxx in the /Users/<your account>/ folder
- Copy the folder to /Library/Displays/Contents/Resources/Overrides/, and you should create the folders by yourself following the same structure first
- Restart your computer
This solution works for recent macOS versions including Big Sur (version 11) and does not require SIP or any security function disabled.