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.