To change the colour of non-working hours:
Go to Settings -> My Settings
Scroll to the Diary Settings section
Click on the colour picker dropdown and choose a colour
Click on Save
You can see it in action below:

Go to Settings -> My Settings
Scroll to the Diary Settings section
Click on the colour picker dropdown and choose a colour
Click on Save
You can see it in action below:

Updated on: 06 / 07 / 2022