Does anyone know what color the passenger cars were painted to go with the new color? Or did GWR, LMS, and SR keep their passenger cars the same colors?
Keep in mind that in general railways in the UK didn’t paint their passenger cars to match their locomotive colors all the time…so say a green engine pulling maroon passenger cars etc. wasn’t uncommon. I think some railways even used different colors on different types of coaches (different classes) so you might regularly see more than one paint scheme on a train.
Remember too that I believe the BR blue steam engine scheme only was used for a couple of years before it was changed to what I think is called “malachite green” which is a fairly dark green - similar to automobile “British racing green”.