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That's the simplest, but you could also use 赤韮 for example, which is literally "aka" (red) + "nira/negi" (leek, onion, shallot), but apparently is also read as Akane, and probably taken as the same meaning. Or you could use Hiragana or Katakana instead, and I've also seen people use combinations of the different writing systems, apparently just to be distinctive.