my hydrangea is suffering, can anyone suggest what is wrong with it and how do I treat it?
That's quite normal autumnal colouring - gorgeous faded shades of mauves and sometimes creams and blue/greens too. Nothing for you to do at this time of year. The faded flower heads provide winter interest and protect next years buds that form below them. Deadheading and any pruning should be done when buds start to swell in the spring.