That's just the Background Color from the category's edit page in the admin panel.
You can use the custom css section in the ACP to customize it, just give the navigation items a custom class in the class field. Then use css to target that.
You need a custom plugin and/or theme to add new fields to categories.
@baris Using the below site, reminding me of just how powerful Chrome Developers tools are, I was able to Copy As Curl the specific PUT command.
Then using the same command and just changing the CID, I confirmed the same command works for all of them.
This is what ended up working, it includes all the recorded headers, of which some will be removed as not necessary:
thanks its very useful
I found the solution. Thanks!!!