How to change black
Did you check /admin/settings/reputation, maybe the reputation setting is higher than 1 which would prevent new users from uploading profile pictures.
@inna you'll want to generate an SSL certificate with Let's Encrypt (you can see the directions on their website)
Please open an issue on our github tracker.
All you should really need to do is change the url value in config.json and change the server name in your reverse proxy.
This is not possible yet we will add it in the next release. https://github.com/NodeBB/NodeBB/issues/5888