Mm, I think I understand.
Here is what I would do:
1 have one characteristic called "topping" with the values "no topping", "topping1", "topping2",etc.
Then, create a product and attach that topping characteristic to it. Then, click on the "manage variants" button to specify the price of each variant (product+topping selection).
Then, create custom item field (only in the business edition of hikashop) called color as a dropdown with the values "red","blue",etc in the menu Display->Custom fields.
On the product page, of each of your cakes, the user will be able to select the topping he wants, the color and the quantity and click on the add to cart button to add it to the cart with the corresponding color and topping.
Would that meet your needs ?