I have found that it changes gradually because the phenol groups react with the base and in water, in acidic solutions it turns orange (lack of free electron pairs so less chromofore groups) and violet in a basic solution (too many free electron pairs, a lot of chromofore groups)
So you were spot on with the phenols!
That leaves me with these questions:
That the structure of carmic acid is great for bonding metal complexes but what makes it so great? I know the double bonded oxygen and phenol groups have lone electron pairs (negative) and aluminum is a positive ion but is that the only reason it forms metal complexes easily?
Alizarin is build from the same quinone, they are actually quite similar
I'm gonna read more about it tomorrow