Hogwarts Express train set (Hornby)
A new, boxed Hornby Hogwarts Express train set.
The set is currently being "kept good" in storage, and is not on display.
The Hogwarts Express is a 4-6-0 Hall Class steam locomotive model number GWR 5900. It is quite impressive.
Although the locomotive used in the films is a correct Hall Class locomotive repainted and renamed "Hogwarts Castle" (the real locomotive used in the films is 5972 "Olton Hall"), the model made by Hornby is actually of a Castle Class locomotive.
In reality, the Castle Class and Hall class look practically identical, the only real visual difference being that the Castle Class had its cylinders set a little further back along its body, requiring feeder steam pipes that were "S"-shaped rather than straight.
Some railway enthusiasts' initial reaction to Hogwarts Castle was that it was a completely wrong colour, as the GWR tended to use green and gold, However, this is explained in the books, as the locomotive is built at the GWR works and then taken away, with all who worked on it having their memories of the episode erased. This is used to explain how the locomotive exists outside the official listings of built locomotives.
Since the ficticious "appropriated" loco is not meant to be part of the GWR, or operated by the GWR, there is no obvious reason for it to be in GWR colours.