Not just on preserved content, though it is most notable there. It also occurs on Sandpatch Grade near Hyndman, including a tunnel that turns your train green for a few moments.
Anything snow covered at night on HRR and RRO, even the BR422 and 425 roofs have it, also the drivers desks as said above. It's only lately that I've noticed it in dusk conditions too. I noticed it on the drives desk of the MP36 too.
For me, this is the main reason to avoid the MP36. It looks like a whole lot of fingerprints, which are illuminated with black light ... horrible.