It's one of the issues when you elect to go with route branding to that extent (rather than just having some vinyls on a standard livery). The arguments on that are long standing. TrentBarton, in the rare times I head through their territory, seem to execute it better than most.
What helps there is that Trent Barton don’t have the secondary school/tenders fleet, as that is covered by Notts & Derby. If you include that fleet you regularly see buses in various old Trent Barton branded liveries being used.
It’s worth noting Transdev generally make good older liveries. The Coastliner deckers at Rosso have revived matching blue Rosso fleetnames and branding, so they look decent.