That's just the Background Color from the category's edit page in the admin panel.
Re: Permissions to create category except for Admin user
I found this permission is only for admin.
If we want all users can create categories, is that possible
You can hide it by using custom css in the ACP.
You are right. I was fixed enabling Custom SMTP and set port 25 and all parameters there:
It sounds like your database is corrupted. I recommend reinstalling nodebb from scratch.
What is not working? Are you receiving an error? Are there any errors in the nodebb log file?