I have an upcoming cake orders for a sofia the first cake & the customer brought me a little toy/figurine to put on the cake. She wants me to match the color of the cake to the color of Sofias dress. It looks pearlized so it's hard to tell what shade of purple it is. What color do you use to make that purple like her dress?

It looks like a fairly pale purple, that leans more towards blue than red.  Start with a light purple and add whatever you need to bring it to the hue of the dress.