Hmmm, maybe not. I think kg! is saying that hydrangea leaves
are turning pink, not that the hydrangea blooms are pink. The pictures are not of sepals that are both green and pink.
There is a rare disease called Virescence that may be happening here. Symptoms of this disease include hydrangea sepals that normally should be shades of pink/white/blue/purple but generate leafy structures which turn green or partly green. So what you are seeing pink-green in the picture is the infected sepals of the blooms!
In time, the plants become stunted, with these leafy looking shoots growing from the sepals
. Eventually, these plants decline and die (not quickly, some may be ok for months or even a few years but will not last like -say- 50+ years like a hydrangea could if given proper care.
If what I described sounds like that, you may want get your money back as there is no treatment or cure.
If this is it, there is no cure. Infected plants should be discarded. Parasitic micro-organisms (like bacteria but called MLOs) are usually the culprits. They are sometimes spread by other insects so minimize cuts that allow entry into the insides of the plant and try to maintain good insect control.
More info: https://extension.psu.edu/pests/plant-di ... a-diseases
https://www.apsnet.org/publications/phy ... 05_608.PDF