Natural colours - are there any that are stable at pH 7-10.5?
I am developing dentifrice to a natural standard (COSMOS, Ecocert, Natrue, Wholefoods etc) and looking for natural colours that would be stable in pH ranges from 7 (silicon dioxide gels) to about 10.5 (calcium carbonate base).
Aside from either Silicon dioxide or calcium carbonate the other main ingredients are sorbitol solution, glycerol and water.
Does anyone have any suggestions what colours I can use or where I may find the resources to find the answers? Aside from Sodium Copper Chlorophyllin, I have no other suggestions.