I realize this has nothing to do with roofs, but for those of you who clean other things, thought I'd pass this along.
Knowing that eggs can remove paint from siding and vehicles (I had it happen to my car years ago), I decided to do some research on how to safely remove the remnants from mischievous goblins and ghouls. I studied the topic on several of the industry forums, found some DIY articles (which I later found were primarily wrong), then stumbled across an article from Popular Mechanics that interviewed several food service professionals who have to remove eggs from surfaces on a daily basis. Hope it's helpful. http://www.ecleanmag.com/hire-a-professional-to-removing-halloween-eggings-from-siding-or-windows-2013-10-30/
We often use SH on egg and it seems to work fine. We clean it off student accommodation (windows) every year after it has been on for ages and it comes off with a bit of a scrub. We normally wet the egg with the SH and leave it dwell for a minute or two. On the rough dashed walls it seems to work well on the egg that is gone black.