THC/BET was either Tilling red or Tilling green (and that was what subsequently was reflected in poppy red or leaf green).
What about Midland General blue, or Brighton Hove & District and Cheltenham District reds? And although I think Mansfield District did adopt Tilling green on nationalisation it retained the distinct Balfour-Beatty application.
So for the other BET companies, you had mainly red fleets of Red (perhaps different shades, and different amounts of cream relief) with Northern, Ribble, PMT, Trent, East Kent, Devon General, Western Welsh, South Wales, Midland Red. There were some green liveries with dark green (M&D) and apple green (Southdown) and something like British racing green (Tyneside) but blue was confined to Sunderland District and East Yorkshire IIRC.
BET red fleets used a range of different reds (although some, such as "BET crimson", were common to more than one fleet. Blue was also used by Stratford Blue (bit of a clue in the name) and County - and East Yorkshire used indigo for buses and a mid-blue for dual-purpose vehicles and coaches.