Actually, not true.  Check pg 426-427 in World Of Irises. The Xanthophylls are higher order pigments derived from carotenes. Found in plastids. Eleven of them  have been found in iris as well as the four basic carotenes.

Only the one anthocyanin has been found, delphinidin , in many different forms. Plus  several flavanoids, which are also in cell sap (mainly, as are manufactured in cell plasma and then transported to cell sap.)

After having said this, I must point out that fussing over all this is best left to theorists, as trying to use this in hybridizing  doesn't make much  sense, given complexity and in addition having to be concerned re intensity (amount of  these present), plus colour effects from  combinations, plus modification from cell sap ph..

As to modifiers,  I just don't have information at hand. But they interact in various ways, including  forming complex   stacking of anthocyanin molecules, which effect how much anthocyanin can fit into solution. There is information on these, but how relevant to iris is another step. Research on this is just not there.

Best bet for you breeding program with anthocyanin pink amoena is to do a hot water pigment extraction to see what base cartenoid pigment is there. And then select parents accordingly.  Should be something with  matching base cartenoid pigment. As anthocyanin is dominant and amoena is dominant so  will carry over to offspring, and is not needed in  other parent. So you can perhaps use a very nice white  for instance, or a pale lavender etc.

Chuck Chapman