This is lichen on a rock at the beach. It piques my curiosity how these shapes form on the beach boulders. They vary in color from a vibrant green, like algae, to a dull sulfur-yellow, usually changing colors depending on their proximity to deformations in the rock. In some places, there are holes in the rock or exposed quartz deposites that seem to be reddening the otherwise green growth. Taken with a macro lens on my smartphone. I went to the beach specifically to find something like this.