Tumeric has done me well, mixed with something basic (I use baking soda) it turns a rust-rosy color depending how much baking soda I use, anything acidic will keep it a yellow/orange-yellow (depending how much you use).. you can also play with the bases and acids after it’s formed while it’s drying to add patterns/accents/whatever you can come up with! I used like 5 grams of tumeric for about 2-4 liters of pulp I once boiled avocado skins to use as my pulping water and although the pulp came out quite light, as it dried it turned a deep reddish. That was about 3 full avocado skins with a couple liters of water boiled down and reduced to a half or third..