While the coloring of your yorkies coat will change; the coat type will not. There are 3 types of coats, cotton, wooly, and silky, or a mixture. See frequently asked questions:
http://www.yorkietalk.com/forums/showthread.php?t=16045 "The puppies with woolly and cottony coats, although growing great length and heaviness fast, never attain the correct visual colors. Their qualities – thick heavy, downy, and soft – deter or dull any light rays from proper play on the hairs."
So a puppy with a cotton coat will never grow a silky coat. There are products that you can use to make the cotton coat more manageable.