Help comb blackening

Ali brought a chicken home from the farm today, think it's a Orpington Blue  , she's over a year old and the comb and wattle are starting to go a darker red/black. 

I had a word with the farmer today who was amazed it was still alive.  Apparently she came home to me because, 'mum's a complimentary therapist thingy',  .  I've had a look on the tips on the forum and the chicken may be lacking in oxygen uptake anyone got experience of this?