For all of Final Fantasy history, we have only known of White, Black, Red, and Blue Magic. Green Magic was an introduction in the series that is underutilized, and honestly it rings right off the tongue. Having a fifth "green" colored magic job with its own flare to how it uses magic, would be an incredible idea, and I hope even if it turns out to be just fan speculation, that we get it in a future expansion.
The job barely has an identity, but a few side games have dared to create it, and I think that the whole clover mage aesthetic is just down right lovely.