Chiltern had a variant of it that looked more modern for a bit, blue around the windows and a red stripe underneath. The red was removed at the last change though.
I think the red still works as a stripe, or a motif, however I'd move away from painting whole things with it.
Blue lamp posts would probably look ok, and that's a colour used by a lot of TOCs anyway.
Or maybe even a light grey for some things. But yes, blue would be a good shout.
I'd have made more of the route badges, which would have been well embedded in the public consciousness by now. You might even be able to do a line in Kent Link "merch", for example.
