“Distracting” could also be said about the thumbnails they are also in colours. To me, it’s a completely different work: being in the library and organize it or editing images. Honestly, I never got my head around that reasoning: colours are an important factor of organizing traffic or bring people to the right airplane. Imagine all traffic signs would be grey to not distract from the landscape :D.
Anyway, in my opinion it was a very stupid design decision and so far nobody delivered some logical, comprehensive basics about that. I say “some people need the colours to navigate quicker”. And the larger the library, the more important becomes a quick navigation.