Black/Grey Instead of Pink

[feralpigeon]

I've recently picked up several ferals for different reasons, or at least apparent ones. When I opened their beaks to examine the condition of the inside of their mouths, they have a grey/black appearance for at least a quarter of an inch from the tip of the beak into the interior of mouth, and sometimes more. These would be several different birds w/very different circumstances and appearance in terms of overall demeanor/condition.

Anyone want to venture an opinion on why this coloration as opposed to the pink?

Thanks,

fp