NHM: can you guess what it is?

I imagine that it isn't entirely obvious...
This is the view between two narrowly spaced units in a rolling stack.
I was walking in the old general herbarium, and stopped to peer between the cabinet units in the rather unevenly spaced rolling stacks: I was rather taken by the strange bands of colour reflecting off the surfaces, and the geometric, slightly kaleidoscopic appearance of all the regular lines and reflections.
Random, but hey ho; 'twas quite fun exploring the shapes and colours, and the scene looked very different from the other end of the same space (due to the directional lighting)...