folks on here know far more than me...
but I was told that fondant is shelf stable for months. (it's sold on store shelves that way)
also, I believe that you can get white butter from specialty stores, but I have gone to look for it yet.
The butter does give the icing a bit of a yellow tinge, but a tip that someone gave on here a few months back, was to add just the slightest amount of purple "paste" food coloring. Believe it or not, that will whiten your yellowish BC icing. I'll try to find that thread because it has so many great tips.
Maybe I don't see so well, but...
I have used the violet to combat the yellow in the butter. However, if I mix the buttercream for about 5 minutes, something magic happens 
and the buttercream appears completely white to me! I use Great Value butter, so perhaps it isn't quite as yellow as some, I don't know.
i found out about two years ago that the longer you whip butter the whiter it gets. I use IMBC for almost all my cakes and if you look at my pics you'll see that my icing, although not white white, it's pretty close. I also use real vanilla in my recipes. I whip it right in with the butter.
I find that my customers will sacrifice the white color for the taste. Butter BC tastes so much better than shortening BC, IMO. You can also add a teaspoon of wilton white-white in with the butter while your whipping. It will make it even whiter.
I don't have trouble with coloring the IMBC made with butter.
kelleygirl
Yes, IMBC stands for Italian Meringue Butter Cream. The Cake Bible calls it Mousseline Buttercream. Same thing. It tastes wonderful and is super smooth.
It may be just my perception, but I think unsalted butter is a little whiter than salted butter - I typically use either Land O Lakes or Giant (depends on what's on sale).
I'm an all-butter buttercream kinda gal, and I also only use real vanilla, no matter if I'm making a SMBC or an American. The flavor definately makes up for it not being white-white, but I also don't do wedding cakes, which is where that seems to matter most.
I use 1/2 butter 1/2 shortening in my buttercream, but add very little powdered sugar(relatively speaking). I find too, that if I whip it long enough, it isn't yellow anymore! I use salted butter, and real, brown, vanilla. The only thing I find to be a problem is that my BC doesn't crust. I use a hot spatula to smooth it while it is very cold. It definitely tastes better than all shortening, at least to me!
I'm making my first fondant cake this week....
i'm adding the buttercream first. do i wait a day or so for it to dry before i add the fondant? i read that you should start a cake with fondant about 2 days in advance....
thank you soooo much for any suggestions.
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