There was a question a few posts back about the livery of WLWR wagons, the 2 in Ernie Sheperds book from the Gloucester Carriage and Wagon Co are shown varnished timber with black ironwork and lettering.
Here is one of the cattle trucks in service still with the black lettering and presumeably the varnished timber weathered down so that it looks grey.
All the other wagons in these photos and others are lettered in white so presumeably it was just the GWC batch.
Donkey 01
Donkey 02
I have put both links in as the people have moved around between photos uncovering different bits of the wagons.
The HMRS have the underframe drawing for these cattle vans
Cattle van underframe