I think meeching means the RailBlue period of the UK ships which used to have a similar livery before 1964/65 when they all got the new BR livery and, a few years later still, Sealink.
The Belgians stuck with black hulls and buff funnels until the mid-80s but these also ended up being 'defaced' at least from the 70s.
I'm tempted to agree with Finnpartner and say it started when Robin of Sherwood bought Sealink for peanuts, but hhv is quite right. 1965 and the big colour change. Those 'monastral blue' hulls never looked that good, IMHO. At least in Newhaven, we kept the buff funnels, albeit with the addition of the route's Houseflag.