Sorry of this has been done before.
How many buses are painted in the liveries of undertakings that merged into the current company
First Leicester have a bus in Leicester City Transport colours
First Leeds have a bus in West Yorkshire Road Car Co colours
and one of the buses they have for the leeds skipton run has a 'Samuel Ledgeard' banner above the distination display at the front.
Any more?
First West of England have a vehicle in Badgerline 2 colours (though they have subsequently now done a modern retake on Badgerline for Weston locals)
First Leicester had two vehicles representing different eras?
First Potteries have quite a few vehicles in different liveries representing different eras (e.g. BET era, post dereg)
First West Yorkshire have a number of vehicles as well WYRCC with Huddersfield Corp, Halifax Corp, Bradford Corp, Yorkshire Rider, Rider York - they also have a lot of named vehicles such as the Ledgard one
First South Yorkshire have buses in Rotherham, Sheffield (x2) and Doncaster Corp plus South Yorkshire PTE
First Midland Red had two in Midland Red colours - the 1960s era has just been repainted into standard colours on transfer but the decker with BMMO colours remains
First Essex have one in Westcliff on Sea colours
First Eastern Counties have quite a few with Great Yarmouth and Lowestoft Corps, Eastern Counties post dereg x4, and even Flying Banana
First Greater Manchester did have all their constituent ancestor fleets represented (including LUT) but they've all be repainted IIRC. Similarly, First Kernow did have ones in GWR and WNOC colours but now gone. First Cymru similarly had a number repainted in United Welsh, Llanelly (not a typo) & District but a number have since been withdrawn
