Bleaching and decolourisation of cheeses coloured with Annatto is fairly well understood and relatively common. Less common is bleaching in natural cheeses. 

Carotene is the pigment responsible for colour in these cheeses.

The image below shows natural Cheddar cheese (labelled as mature) displaying bleaching around the edges. The cheese was purchased by me from a local supermarket a few days ago. It had a best before date of the 7th March.

Bleaching is normally caused by oxidation of the carotene.

A retail pack problem caused by packaging having a high permeability to oxygen, high intensity florescent light or some other reason? Comments welcome.