There's Red and Blue, but why not Yellow?

[Thimacek]

You might propose that Yellow Mage be an alternate name for something else. The Summoner, for example, or Mime. I wonder if Mime could use an update? Haven't checked it in a while. Hmmm.

As far as Green Magic goes, I wonder if there could be a Green Mage archetype that fits both White Mage and Black Mage classes and grants limited enhancing/enfeebling spells from the opposing class?

Tbh, from what I've seen both the White Mage and the Black Mage spell lists include a fair amount of both enhancing and enfeebling spells, so I think the current Green Mage works alright with both (and also with Blue Mages, perhaps even better for them!).