I've always thought they look more brassy in the actual Cave scene. Certainly more metallic/reflective. This is why up until now, I've exclusively used brass for the rails. Just recently though, I've been looking at the MoM pictures and can't get away from the fact that they match those traces so closely, and that I'd expect painted metal to have more wear. Especially on a part of the prop that is so exposed.
One thing that I don't think has been mentioned yet and was discussed in earlier conversions is the damage. The Hero prop was almost certainly dropped and suffered significant damage between filming and exhibition.
This has always made me wonder if the rails were replaced as part of the repair, which might explain the inconsistency between the shiny on screen look and the way it looks today? The material is so very thin. Once something perfectly straight is bent out of shape, it's easier to start with a new piece that to attempt to straighten it out again.
Maybe it had to be repaired without having access to the same shop/materials?