Iridescence caused by a layer of an unknown substance on these lichens. In each case, the first photo was taken with direct sunlight shining on the lichen, whereas I blocked the sun in the second picture. This way, only diffuse light would shine on the lichens, removing the iridescence effect.
[ direct light || diffuse light ] ⇛ (2015-03-14)
[ direct light || diffuse light ] ⇛ (2016-04-09)
[ direct light || diffuse light ] ⇛ A close-up of a part that was out of focus. (2016-04-09)