The authors thank Dr. Silvia Vignolini and Dr. Beverly J. Glover for their helpful comments on the manuscript, Tom Blough for building a custom-made, remote-controlled micro-stretcher for fiber band-gap tuning and Dr. Paula Rudall and Dr. Stuart Blackman for kindly providing some M. nobilis fruit samples to start the investigation. Financial support from the US Air Force Office of Scientific Research Multidisciplinary University Research Initiative under award numbers FA9550-09-1-0669-DOD35CAP, FA9550-10-1-0020 and the UK Engineering and Physical Sciences Research Council EP/G060649/1 is gratefully acknowledged. M.Ko. acknowledges the financial support from the Alexander von Humboldt Foundation in form of a Feodor Lynen postdoctoral research fellowship. This work was performed in part at the Center for Nanoscale Systems (CNS), a member of the National Nanotechnology Infrastructure Network (NNIN), which is supported by the National Science Foundation under NSF award no. ECS-0335765. CNS is part of Harvard University.