Hi, I am with Jade......I have never seen anything like that before either, and I've had cats a long time. The green claws are a new one to me. = ( I do wonder if this could be some sort of fungal infection. When people get fungal infections of the nails they turn green, so maybe it's possible w/ kitties? Just a thought! I'd definitely take kitty in to the vets. If you do, please come back and let us know what this is-you'd be teaching us something on here! LOL
Hi, I really have no experience with something like this, but just from reading your post, I would get kitty to the vet just in case it IS an infection. I suppose it could be from your furniture since the discoloration is near the end of the nail, but not being able to actually see it myself, it's hard to say.
If YOU are worried, then you are the best judge. Go ahead and have him checked for your own peace of mind.