dogs paw pads

Question
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Followup To
Question -
I have a Shih Tzu, 1 year old.  To give you a  little background......We have had trouble with Rikko's diet and now have him on a kibble food that we purchase from the vet.  Hill's Prescription Diet.  He seems to be doing fine, I was cooking chicken or beef and rice or potatoes with carrots and peas for him.  He is a very finikey eater who also has trouble with Anal Glands.  His stool is now normal, hard and dry.
Now the problem.....I have looked at a lot of dog's paw pads and all are black.  Rikko's are not and I'm sure that they used to be.  They are black around the edges and a pinky colour in the centre.  His paw's also seem to be very sensitive to cold (floors) and to rough surfaces such as gravely pathways.  Do you think this is diet and how long does it usually take for a new diet to affect changes?  
Thankyou for any information or help you can give me, I do appreciate it.
Aileen   
Answer -
Hi Aileen!  Has he been on any rough surfaces lately and do his paw pads seem sensative?  Does he try holding them up like they hurt and etc?

Follow up question........no, he doesn't hold them up and act like they are sore.  He just seems to be very sensitive to cold floors, runs to the carpet or his basket and curls them up under him.  Sometimes he appears not to like to walk on gravely surfaces.  Also, what is you advice on feeding?  
Thanks Aileen


Answer
It could possibly be allergies but most likely it's just his skin coloring changeing as he is growing if he is still a pup.  As for his diet, the best food I have found so far has been Flint River Ranch.  You have to order it online but it's a great food and wonderful for their coats and etc.