Weird discolouration of carbon frame
Edited see comments below

This is from the BMC website. Cut-and-paste for reference.


  BMC’s frames are made mostly using UD carbon fibre. UD stands for
  unidirectional. Unlike more traditional carbon fibre products that use
  a woven carbon finish (criss-crossed finish like a woven piece of
  material), UD carbon is literally a piece of carbon material with the
  filaments all running in one direction. BMC’s frames are made from
  many different pieces of UD carbon that are woven together, similar to
  what is done in textile production. Some of our frames contain around
  350 individual pieces of carbon fibre that go into the mould before
  heating and curing takes place. These material sheets - some very
  small, some very large - are laid at different angles across each
  other to achieve different results: torsional strength, compliance
  areas, rigidity, and so on. The layup of these sheets is extremely
  important to the end result. This is actually the art of building a
  carbon fibre frame.
  
  On our unpainted frames, you  can see the result of these carbon fibre
  sheets overlapping each other through the clear coat covering the
  frame. We are actually very proud to be able to show this real effect
  on our frames. It shows not only the true workmanship of the frame,
  but also the resulting quality as the frame exits our moulds. Many
  bike manufacturers prefer to paint their frames because there are
  often many imperfections in the finish that need to be re-worked using
  a filler before waiting for it to dry, sanding it, and then giving it
  a final paint job (a bit like a panel shop). This is a cheaper way to
  finish the frames, ensures you have no reject quantity, and allows you
  to use less stringent production techniques.
  
  On unpainted BMC frames, when you look 'into' the frame, you see the
  actual quality of what’s on the inside – we are showing you our finish
  and quality and we are very proud of that.