@nielslyngsoe it works using willUpdate. I wonder if it is possible to check on specific property change in settings block as it currently react on any change in settings properties.
Besides that it update the background color immediately after selection, which is okay, but I think it ideally may be better to reflect the changes after submit from modal.
However it doesn’t seem “Close” or “Update” from modal make a difference anyway - in both cases property is updated and persisted after “Save & Publish”.