Discolouration in P-L P Y-S

Discolouration in P-L P Y-S

Observation - Discolouration in P-L P Y-S - UK and Ireland. Description: I found this discoloured P-L P Y-S in a gap in our patio yesterday. Does anyone know why it's discoloured?

I found this discoloured P-L P Y-S in a gap in our patio yesterday. Does anyone know why it's discoloured?