Sorry DiesAL (love the name!), I should have been a little clearer. I was referring to BR Mark 1 coaches. Very few pre-nationalisation types lasted beyond the mid-sixties, and only a handful went into blue and grey (some Hawksworth ones on the WR, Staniers on the LMR and ScR, and a few Gresley and Thompson coaches on the ER and ScR - a few got swapped between regions too).
The chocolate and cream Mk 1 coaches on the WR were mainly used on the crack expresses but were also being phased out (repainted maroon or even straight into blue and grey) by 1964/65 or thereabouts, cetainly only a very few with first class (FKs, FOs, BCKs and CKs) lasted long enough to gain yellow cant rail bands, which started to be applied to green or maroon stock in around 1963.
Mark 2 coaches might include the odd FK in maroon but all others would be blue and grey, and even those early FKs would probably have been blue and grey by the early '70s (educated guess here, though!).
Pre-Nationalisation types on the Southern remained green through to their ends of life, as far as I know - the only ex-Southern Railway stock that received blue, or blue and grey were the utility vans (PMVs, CCTs, BYs, etc) and the Maunsell mail coaches, plus some of the EMUs. None of those really fit the question you were asking.
Edit: Addendum: the Hymek was a relatively late type and would not have hauled too many crimson and cream coaches in their early lives.
I have tried to keep the answer simple but, as you can see, the subject of liveries gets quite complicated because there was never a straight change-over; painting thousands of items of stock takes many, many years to complete!