Made another batch of cupcakes. This time I used "Butt Naked" fragrance oil to the cake part of 4 cupcakes. Description for this fragrance oil includes the fact that it contains vanillin which will discolor soaps to shades of brown. The above picture showed the darkening of the base as expected.
Ingredients include Olive oil, Palm oil, Coconut oil, Castor oil and Cocoa butter. I used titanium dioxide for the white and neon pink for the frosting. Fragranced with Butt Naked for the brown base and Aromatherapy Energy for the frosting and some of the cupcakes as well.
This picture is just to show how the fragrance oil darken the soap on the left.