I have a jigsaw of GWR King class "King George V" in the experimental BR blue livery. There was a card kit available years ago of a Merchant Navy class in the same livery along with, I think, a Duchess, also deep blue.

This was in the early days of BR, soon after the formation in 1948, and a number of experimental colours were tried out. There was a model of "Brecon Castle" on sale in OO in the pale green livery at one time.

It all happened again a few years later trying out different colours for diesels, blue, green, maroon and sand liveries on the D1000s.