I made that cake last week using purple ganache. The ratio for most white chocolate ganache is 3:1 . Little bit of corn sirup is suppose to add some shine to the ganache. (Not sure if it realy add anything though...)
Here is the recipe
1 1/2 cup white chocolate
1/2 cup heavy whipping cream
1tbsp clear corn sirup
(I had more than enough ganache for my 8inches cake. 1cup chocolate and 1/3 cup of cream would have been ok)
For the color, I've use violet wilton candy color.
https://www.cakecentral.com/gallery/i/3416186/emoji-cake
Wilton makes Candy Melts with glitter in them, but I don't know if they have purple.
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