Tango’s eyes aren’t originally red, they were turned red from exposure to redstone (possibly from his tendency to carry redstone components in his mouth if his hands are busy or if he’s traversing tightly packed redstone noodles in full dragon form causing him to ingest bits of redstone fairly regularly), and therefore glow when he is in contact with powered redstone of any kind. He didn’t notice this until someone else pointed it out.
He has now also gained a taste for eating red stone, so it’s unlikely to fade anytime soon.
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