"Should we expect a blue one next?"

Nope! That coloring is not in the plant's genetics.

So I assume pink is in the genetics?

A precursor to some of the modern pink Annabelles.

https://www.quackingrassnursery.com/plant/Hydrangea-arborescens-Eco-Pink-Puff

It'll be interesting to see if anything comes out of this work. I would assume the goal is to get the pH dependent blue coloring into a plant that act more like an Annabelle and blooms on new wood.

https://journals.ashs.org/hortsci/view/journals/hortsci/50/12/article-p1765.xml

And I would amend my original comment to say that they can GMO just about anything these days so perhaps possible. Although why any breeder would spend all the years and the multiple millions it costs to genetically engineer a new plant just for color is beyond me. The return is just not there.

Some true blues would be interesting; so would be a purple color. Plants like that would end up producing a very winter hardy and bloom reliable alternative to mopheads.