User blog comment:LastationLover5000/Fairy Tail Episode 156 - Sky Labyrinth/@comment-5004454-20121114153529/@comment-5004454-20121114184631

Lol, yes they do, they're seals. They strengthen the normal lightning, which turns it black. Why else would they tattoo the kanji for lightning in their body? For that matter, how else would Kingin brother possibly recognise them? There must be something special to those tattoos, since anyone can make the same tattoo and pretend they can use black lightning. So far, seals are the only thing in Naruto that can provide effects with ink (amongst other things).