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What is up with Jonny d'Ville's scar/makeup?

So I'm new to the fandom, and I cannot figure out for the life of me what the hell Jonny D'Ville's lightning marks are. Is it just makeup? Scars? A genetic defect to do with his species? Veins?? I can't find a definitive source (yes I tried the wiki) Please help I'm so lost lmao.