Two comments on the Red livery.
This was discussed on the GWR ehgroup some time ago. As a result, someone did some tests mimicing the orthochromatic film available at the time of the transition and demonstrated that it was impossible to distinguish the colours from Black and White photographs.
Secondly, in "The Locomotive" Volume 1, No. 3, March 1896 (part of a study of virtually all the major Companies liveries, and quite a few of the smaller, the author states:
"A light red colour is adopted for the wagon stock with white lettering but the goods brakes are a dark grey."
Since this is contemporary observation, it must mean that the change was later than 1896.