Something to consider that's hopefully not too difficult, but would be helpful for people with multiple hubs (possibly also for "branding" in commercial uses).
When I say "headers/tabs", I'm thinking about (as an example), say the "bar" at the top that is currently black and, possibly, the list on the left side (Rooms/Devices/Dashboards/...).
By allowing user-specified colors to be set for each hub, it would make it easier to tell which hub's interface you were viewing. E.g, one might be blue, one might be green.
Note: Ideally, the text and other items in that bar that are currently white could switch between white & black depending on the color (for better visibility).