Ooooh...it's an exciting time waiting to see what color your baby will be, isn't it? I remember the same thing when I first brought Sophie home.
However, you may have a very long wait!
It can be up to three years till a Yorkie has his/her final coat. But there is a hint or two you can look for.
If she is black on her saddle, can you see that her roots are beginning to lighten? If not, then she will probably remain black on her saddle. My Sophie is that way and she has remained the richest color of black, yet underneath she has some silver. Her face went from mostly black to the richest colors of gold/auburn. Some heads and faces will go totally silver. And again, you will see this first begin to happen at the roots of the hair.
I have the same thing with my Biewer a la Pom Pons. Although my one was mostly white when I first brought him home, he is now getting black streaks through the white where ever he has a black freckle (Spot) on his little pink skin. It's called "ticking". And it will be a good three years too until he has his final coat!
Hope that helps to give you a little something to watch for!
Have fun!