Stain? Ghost?

Searching to find out why leaves makes these stains on concrete, I find a lot of webpages dedicated to getting rid of them (bleach, blech!). I love the things! And find them deeply satisfying. In a cursory search, I didn’t get much further than the organic pigments in the leaf become embedded in the concrete’s micropores. Put another way, you can pave paradise, but paradise won’t let you forget it.