I know the box says to use shortening instead of butter to make it whiter, but I HATE the taste of shortening in icing (& so does the cake recipient). Any other ideas? This is for my neice's baby shower and I'm doing a quilt cake. (Also have 3 kindergarten graduation cakes to do).

I read a tip here a while ago that worked for me.

I make all-butter buttercream and it has a definite yellow tint to it. I read here that adding a tiny bit of violet food color will counteract the yellow and make the icing white.
It really works! Just don't add too much or you'll get purple icing.

Also, Wilton makes an icing whitener that works well.

Good luck.