Hello-
Interesting discussion, relating to red pigments in Umbilicaria, you might want to check out Grube et al. 1995. There is a brief discussion/speculation of a parasitic Arthonia "inducing" a red pigment defensive response in the host Umbilicaria.
Grube, M., M. Matzer, J. Hafellner. 1995: A preliminary account of the lichenicolous Arthonia species with reddish, K+ reactive pigments. - Lichenologist 27(1): 25-42
-JV