Recipe(tried): Baker's Bakery (not) white frosting

It was originally a combination. Since then I've learned that the original Bakery didn't use any shortening. I had used shortening because of the whiteness of the frosting and decided to try shortening to make it lighter (in color).
Since then I've determined that the yellow comes from the fact that most of the butter you get in the store has food coloring added. So...
If you want white frosting, you can either look for uncolored butter, or use some shortening. Both work, although the mouth feel for the shortening is a bit different.
If you don't worry about the fact that the frosting isn't actually "white" you can use all butter and both the taste and the mouth feel are better.