The good news, cg, is that just about anything goes - although a typical train would have had hardly any two coaches alike, a rake all of one type being inaccurate!
Only one "Woolwich" was ever black, and it was painted thus for the Rosslare - Cork boat train. That's not to say it didn't turn up elsewhere... Probably it did. The black was short lived too. So my first assumption is you are modelling somewhere in the "deep south"!
Others of the class, like all other loco's, were either lined CIE green (in a small number of cases) or the standard unlined battleship grey.
If you model pre-mid-fifties, then everything bar the three 800 class* was grey, including all Woolwiches. So I assume your layout is based late 50s.
So here goes. Your train will have a motley selection of brand new Park Royals and laminates in silver or lighter green if you're closer to 1960/1, but mostly old corridor GSWR stock, and more than a few Bredins. One feature will probably be one of the three clerestory coaches, possibly including the RPSI's twelve-wheeled 861, which was a brake tri-compo built as part of a set for the "Rosslare Express" in 1906.
These older coaches will be in the darker green with the broad light green stripes above and below window level.
A few horse boxes or a parcel van might bring up the rear, and somewhere there is likely to be a 6 wheel passenger brake or mail coach.
Hope this helps.