This would be a good way to subtly “remind” the user which account they’re currently using/logged in as.
This would basically involve either (a) moving the “primary color” widget from the “appearance” section to the “account detail” page; or (b) making the “primary color” widget into a sub-section of its own, and where each account is listed.
I love this idea. I just the other day subbed a bunch of communities on the wrong account because I forgot I switched.