Perhaps it was more of a steam engine than a locomotive but, from the angle that top photo was taken from, it was certainly plum-coloured.
Its trimmings were in other shades, though, including the most glorious scarlet wheels with black and yellow detailing:
Unlike the ferris wheel in the background, the wheels on the steam engine didn’t go round and round; there was certainly movement of a kind, though, which the magic of digital technology has allowed me to turn into perpetual motion in a lovely vintage shade of sepia:
Of course, the real idiom is plumb loco, which has nothing to do with either colour or motion. But where’s the pun in that?