This thread reminds me of what my groomer told me: "Yorkies are like a box of chocolates, you never know whatcha gonna get!"
I took Bailey for her first groom when she was 3 1/2 mos old and all her puppy fur was gone - replaced with silver underneath. As her fur grew back in, the silver turned to the blue/silver and her head turned tan....now she sports the traditional yorkie colors....