You research period colouring agents, and reject those that are rare, exceedingly costly, or toxic. You settle on red sandalwood powder, which is used as a colourant in other recipes in the source where you found your cheesecake*. You mix some in with your marzipan until you are happy with the colour.
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* For example, in the recipe ‘Leche Frys in Lentoun’, http://www.godecookery.com/goderec/grec60.htm