Yes and no.
My own recollections, and those of others, are of all-over spray. I certainly saw H vans, palvans, and also on one occasion one of those outside-horizontal-planked GSR vans newly painted, and they had brown roofs. However photo evidence shows up very clearly what is one of three possible things:
1. Wagon resprayed brown, but not the roof. Unlikely but possible.
2. Some wagons WITH grey roofs - though a lot darker than in the artists' impression of the model.
3. Possibly painted brown, but weathered so badly (like CIE grey or CIE green steam engines, red CDR loco domes and blue GNR domes) that it was impossible to tell what actual paint colour was under the dirt.
(2) and (3) are the most likely, but all-brown was very definitelt there too - I saw it myself.
I'll be ordering some, as they look amazing. When I do, I will take a very deep breath and try to pluck up courage to get them weathered. The roof will be first!
IN traffic, the rich brown tended to "flatten" quite quickly. The heavy marine ply the sides were made of didn't take well to weathering.