Platismatia glauca

Platismatia glauca

Observation - Platismatia glauca - UK and Ireland. Description: Mixed with a bluish Parmelia sulcata in pic 2. Any thoughts on the reddening of the thallus in pic 1?

Mixed with a bluish Parmelia sulcata in pic 2. Any thoughts on the reddening of the thallus in pic 1?