Anthocyanins are a family of pigments. Delphinidin is one member of that family. It refers to the basic molecular structure.  There are several attachment  points for various  sugar and hydroxal molecules, leading to many different forms of delphinidin. 

No chain  of dominance  and many forms can be present in same flower. 

This is without  considering  all the modifiers and co-pigments.

But by far the biggest factor that we need to consider in iris flowers is the AVI  effects. That is the form where delphinidin clumps into a protein complex and makes for dark globules inside vacuole. This is where we change flowers from being lavender-blue, into purple and provide basis for black flowers.

For interest sake, consider that Daylilies have delphinidin, but they just can't get "Blue" daylilies. Only lavender and purple.

Of course we always have some other pigments present.  And these change appearance of the colour in the flower.

Also is  the effects of  ph in cell sap in vacuole. This can be of immense importance.

While a lot of research has been done on pigments, (the chemistry that is ) very little has been done on how these pigments  translate into flower colour.

All things considered, the particular form of delphinidin present  would not likely make a lot of difference in most cases.

One exception is the  "floridor"  form of delphinidin, which is named after the cultivar Floridor . This provided a slate-blue- gray shade. 

Chuck Chapman