Shoot I do that at work for admin vs non-admin logins, or different gmail accounts (personal vs side-biz). Reddit, too -- leave one permanently on night-mode.

IMO should be an SOP for anywhere that you might log in with different accounts.

How many times have you been logged in as root and didn't realize it?

Now that you mention it, I do the same for my dev installation of HN.

It’s a great visual indicator to remind of your active environment. I use it in just about every app that supports it with custom colors aligned with the environment (e.g. blood red for prod or canary yellow for dev). Gmail supports it as well. If you have multiple accounts with an “official” corporate color, it makes it easy to realize which you’re acting upon.