Your plant is fine, irishlc. It sounds like the flowers are doing what hydrangea blooms do as they mature... change colors. Depending on the variety, hydrangea blooms go through a gradual series of color changes as they mature. Green or green mixed with splotches or pink/blue are examples. This color change starts more or less in July and may be followed by yet another color change before the growing season is over. In the case of remontant hydrangeas like Endless Summer, you can deadhead the flowers and get new ones if your weather cooperates and the growing season is long enough.