Yes, a titch of violet combats yellow. If you, look at a colour chart you will see it opposite. Too much and it is the weirdest colour ever!
I’ve heard that it doesn’t take colour as well as american buttercream and doesn’t change that much overnight either. I use fondant more than bc for covering but I have a wedding cake that I am using Sharon Zambitos buttercream on the outside to take a dark navy blue colour but using smbc in the inside for the filling.
