In general, the only hydrangeas that are grafted are tree form or standard trained paniculatas and typically only those from Canadian suppliers. Any shrub forms are not.

As to why the flowers on yours are not uniform in appearance could be due to a number of reasons. Flowers that are produced later in the season may not have the exact appearance of those produced earlier simply because of different growing conditions that arise later in the season. And any cultivated variety has the ability to revert back to the species plant in part.

When you trim some paniculatas while they have flower buds about to open, they may issue new growth and bloom "later" on.

There are some places in Canada that sell grafted hydrangeas but I am not sure what is up with that... ;o)

I'm thinking it could be a

..

The type of hydrangea is a paniculata. Many bloom white and then turn a shsde of pink. On some, white can be preceeded by a lime green color (Limelight, for example) but I doubt yours is one; I am just noting that it is another paniculata bloom color you might see. There is nothing one can do to revert the pinks. You can, however, delay it from blooming. If you delay it long enough then you get no blooms.... If you do not like the white now then you can prune it off. ;o)

The shape and color of the blooms look like Quickfire to me as well. The white flowers have the same form as the pink ones, so I would be inclined to think that they are just ones that were produced later and so haven't matured enough to change color. If you are worried, place a marker such as a colored tag of some kind (yarn?) on those branches and see what they do next year, but if it were mine, I wouldn't be overly concerned.