Hello,
I seem to recall reading somewhere that the LNWR manufactured most of its own materials in house where possible.For instance signal cabins,bricks,bullhead rail,signals,rolling stock, locomotives,wooden station building panels and even workers housing.Far more than any other railway company before or since.I believe they used red english bond brickwork on cabin locking rooms whenever brick built.I have seen a number of colour examples using red brick which also include blue engineers bricks at the base and for the arches of the locking room windows as well as the bullheaded bricks along the lower course of panels,Examples can be seen which are curently in use in various regions of the former west coast main line if you look close up as the details are hard to make out otherwise.LNWR portrayed by Jack Nelson and A Pictorial Record of L.N.W.R. Signalling by Foster, Richard D may have been the sources.There are others which include colour images of LNWR boxes.Look forward to seeing more of your work.
trustytrev.