I don't know the answer but thought I would share a picture of Kodi's claws when we rescued him in October 2010. Somewhat similar looking.
He had been picked up as a stray, then confined in an indoor wet concrete-floored enclosure on deathrow for 30 days, then rescued by a no-kill shelter where he had been for about 90 days, with an outdoor wet concrete floor--wet due to the weather on damp Vancouver Island.
There wasn't any associated health issue, the problem cleared up with good diet, lots of exercise and good living conditions. His claws are nicely white now, solid as a rock too. His foot pads are also good.
I suspect it was stress and poor living conditions that caused the problem for him. I was concerned back then, so took this picture of his foot...
