It's a little known fact that moch of the design and development of military camouflage was developed in Leamington Spa. A new exhibition in the art gallery Concealment and Deception: The Art of the Camoufleurs of Leamington Spa 1939 - 1945 celebraites this as well as providing behind-the-scenes pictures of the artists at work.
I'd assumed that camo was randomly painted but according to the exhibition, there was a lot of planning involved. Scale models were built of major projects and then fitted to a rotating table in the requisitioned roller skating rink. They could then be viewed in different light conditions at all angles to see what worked.
A similar set-up was created in the town museum with a water tank for ships.
Those developing the schemes were artists and so they naturally painted scenes from the job. Above we can see a factory being disguised. The original belongs to the Imperial War Museum and is on load, along with several others, to the exhibition. You can see the full listing here.
Building camouflage isn't something I've seen modelled very often. Presumably the paint hung around for many years after the end of the conflict so those models set in the popular steam/diesel transition era could justify some interesting roof colour, albeit very weathered.