Here is an interesting paper from some years ago, pointing out that multi-spectrum "packets" of light will redshift over distance, as the higher frequencies dissipate faster;

http://fqxi.org/data/forum-attachments/2008CChristov_WaveMotion_45_154_EvolutionWavePackets.pdf

Which would pose further problems with Quantum Theory, as it would mean we are sampling a wave front, not detecting individual photons, that traveled billions of lightyears. So it would mean going back to a "loading, or threshold" theory of quantization.