Yes but they are not exactly reverting to white. The colors fade from pink to a sandy-whiteish color after the blooms fade. It is a normal change in hydrangeas. Depending on the variety, you will see these color changes. Bella Anna, similar to Invincibelle Spirit, also does the same thing.

The flowers on these two plants didn't fade. They didn't flower pink and look exactly like the flowers of the Annabelle we have.

Diane,
It seems to me the same thing happened to my I.S. on a sucker next to the original.