I've heard that the more yellow lichen are a sign of poor air quality. Eversince, I've noticed a lot of lichen in yellow colors, but only in the cities.It is lichen, a symbiotic relationship between an algae and and fungus.
It can actually be a sign of decent air quality.
Where I live in the Shenandoah Valley, lichen is quite common and found everywhere. I have never seen it choke out buds.The only problem with lichen is when covers young branches, if its very thick it could choke out the buds, in the main trunk it dont make any harm just stetical