The Case of The Mystery Purple Foot

So here is a mystery for you all. I came home this evening and let Tinker the little scamp out in the garden. As I watched him run I noticed he had a purple foot! His hair is purple on the bottom of his foot. I tried to take some pics but they came out very dark – it’s a much brighter purple. There are no purple foot marks around the house and nothing around the garden… He was out for a little while last night, but I didnt notice anything then. He has been in all day… So how did he get 1 purple foot? Ideas on a postcard or comment PLEASE!