is it a known Problem? Since a few weeks ago i can´t change the colour of my Forms layout.
I was able to adjust coulour before and got a "HEX" now. (As on screenshot)
Hex will let you specify a specific colour that you want so it's a really great feature to use.
Try using a website like https://htmlcolorcodes.com/color-picker/ and set your colour into the Hex box (e.g. should look like #7ac6d9) to get a result.
The original default colour options should also be available but I find being able to choose any colour I want using Hex is far more beneficial.
Hope that helps?