Well in the early 1970's, which is the era your locos would represent, assuming they are all painted plain blue, the only colour the Mk2's were painted at that time was blue and grey, so for authenticity any other colour is out. I wonder if by compartment stock you actually mean Mk1's? But it does seem that you are running a bit of a mix - you would not have seen a class 35 Hymek along side an Executive/Intercity liveried HST for example. You may not be bothered by that and just want to run authentic trains, even if it passes one that is out of era. Keeping the 'charter' stock blue and grey only will cover most of what you may want to haul it with.