Colorful multiple reflections
The picture shows an ensemble of optical beam splitter cubes illuminated by a flash light. Since their optical coatings are designed for 800 nm reflectivity oscillations of the coating in the VIS range occur. Together with dispersion these oscillations give rise to colorful multiple reflections under different angles. The photo was taken in a darkened room and the beamsplitter cubes were placed on a white sheet of paper. —Dirk C. Heinecke, University of Konstanz, Germany