Zombie Aquaman could use his legion of dead sea monsters to completely shut down civilian sea traffic worldwide. Yes, in terms of the greater war between the colors, he's a footnote, but he's more than capable of ruining life on Earth for any nation that depends, wholly or in part, on the sea. That is in fact all of them. Giant kraken crush ocean liners, undead fish jam the engines of nuclear submarines, sharks eat fishermen and beach goers, and worldwide shipping lanes are not disrupted so much as immediately severed.
Then, when somebody goes into the water to try to deal with Zombie Aquaman and his legion of undead fish, they get eaten by sharks. All the sharks. Ever. Bonus round if it's a low-wattage superhuman response, who go in joking that it's "just Aquaman."