It was straightforward signalling from the USA, as I described above, in fact not the more complex from there, that has gantries with multiple such masts - Mirfield was all single masts. The equipment was actually imported from a mainstream USA supplier, Union Switch & Signal if I am not mistaken, from Pittsburgh, actually George Westinghouse's old company; I don't know how much the UK Westinghouse in Chippenham was involved. Once you understand the principles it was all more understandable. I believe the LMS later discontinued the Advance Caution, the only one with yellow, green and red on the same mast, which was a 5th aspect beyond a UK 4-aspect double yellow, because at the speeds at Mirfield it wasn't necessary.Found this on the Signal Box website. Drivers must have had to know their stuff. So many combinations of red,yellow and green.
How about this one then, a little nearer home, which at night would display you 24 reds, 18 yellows, and two greens :