I don't think she is going bald. Maybe that means she will have silky texture & you just have to be patient for the hair to come in. Sounds like her tan is going to be a light tan. That's what is great about Yorkies. They come in so many colors.
I have 2 pups & the Mom was light tan & light gray, the Dad was black & tan. The pups have different colors in their roots & I am tickled pink. I hope they are different colors because it's very hard to tell them apart! The one's tan coming in is almost creme colored. I love them whatever color they are. Mine aren't for show, they are pets anyway.