Messing with layer blend modes, and not much else.
Fun with Photoshop. Total time, about 3 minutes. I wasn't really expecting anything from it, and it's more of a novelty look than anything else - had it not been a cemetery I would have likely tossed it. I thought it was rather interesting how the paired Exclusion layers managed to leave the ground area virtually unchanged, but totally messed with the sky (i.e. the brighter areas).
Layer blend modes. I will have to look into this--something else with which I am not familiar! Thanks for taking the time to explain!