I am getting some dark, brown or orange or purplish spots in leaves, part of common hydrangea leaf spots that become visible in mid-to-late summer, Called Cercospora Leaf Spots. Typically caused by overhead watering so I minimize the issue by watering the soil always and never the leaves. Cannot be cured so water the soil and maintain the soil as evenly moist as you can.

The stems also turn colors as they either suffer from lack of water or when they begin to prepare for winter. The soil above looks dry. I would dunk it in water and place it in a bigger pot too.

If the area gets windy, this will cause mild breezes that will dry out the leaves and the potting soil so something that blocks the wind and makes sure it gets afternoon shade will also help.

One cousin of mine was a temporary teacher in Barcelona and had this soil moisture issue so work on keeping the soil as evenly moist as you can. Morning sun only; no afternoon or evening sun.