I don't know about you guys, but I wouldn't really consider Geomancy a magic, mostly because it doesn't use Magic Points (in Final Fantasy Tactics).

Also, in the same game, the usage of Geomancy was dependant on whatever landform the Geomancer was in contact with, and couldn't use any element at will. The other magics, however, can be used at any time as long as the caster has enough MP, further diqualifying it.

Then again, there's the Geomancer class in one of the mainstream Final Fantasies, but I've never come in contact with it myself, thus I can't speak for that case.

FFV. No MP cost, picks a random "spell" depending on the background and your level. Mog's dancing is similar, but he can change the background.

I usually consider Black, White, Summoning, and Blue to be the basic categories for FF magic. The differences between those are the most concrete I think. For the sake of making more jobs you can then cut'n'paste spells from those sets into new categories like Red, Time and Yinyang, or alter them slightly for things like !Sword Magic and Dragon Magic. Then there are spell like abilities like ninjutsu (which in FFXI requires tools like squirt guns and caltrops), geomancy (using one's surroundings as an extension of one's self), monk powers (manipulating one's own qi), song and dance.

I remember from playing FFV way too much, that time magic was marked with grey icons (vs. the black icons for Black magic and white icons for White magic)

as far as i know, no collor was ever attributed to summoning or geomancy.
(geomancers FTW)

Actually, I think that Red Magic has one unique spell (at least in FFTA). It is the only magic set with doublecast. Of course, doublecast doesn't use MP, so is it a spell? Who knows.

This should answer all of your questions, and more.

Ninjutsu? FFIV, and Tactics label that as seperate. But I suppose Ninjutsu isn't really magic as much as items combined with spiritual power (so a combonation of magic and items?).

Perhaps Alchemy (magic through items/science. Not invoked through a person's spirit, but still magic in some way.) I suppose, silver would be a color? Or maybe clear...

I think the term gray magic came from people saying that red magic should technically be called gray magic, not realizing that the original design comes from the D&D alignment stuff, red being neutral between good (white) and bad (black).

I think creating a new category called Green Magic is sort've silly, but I guess it's okay, since FFT had the Oracle class with the status changing abilities (and they called it Yin Yang Magic in that game). Green Magic is a better name than Yin Yang Magic.

I'll tell you what they need, is purple. For magic of the funk.

Just think of it, you're sitting there playing Final Funkstasy Tactics, and then your Jimi-class unit wipes your enemies out, by setting his guitar on fire to summon the Soul of the Rock.

James Brown, launching Say it Loud attacks. Clinton-class units, summoning the Mothership.

Kick out the jams, motherfuckers.

Don't even tell me you wouldn't play that game. You know that I don't like it when you tell me lies.

Makes me think of the Pimp class in my game...

But if you're going to throw in purple for funk, may as well throw in pink for pop-magic (as in pop-star). Gets the opposite sex to at first drool over you (paralyze), then do what you want (charm), but if you keep it up to long, they want to kill you (aggro).

It's hard to argue over something like the colors of magic. If you take all of the Final Fantasy games, you'll see so many differences from title to title, you would never get to a point.
And what is "Time Magic" after all? Haste and Slow? I would say, sometimes it's black, sometimes it's white. What should green be? Stats-boost? Like Protect and Shell? Or the other way round? Poison and Sleep?
Is summoning magic or just a natural skill? Depends on the game. I.e. FFVII (magic, I count materia as magic, and all these nice colors... summoning was red, right?), FFIX (natural skill and magic), FFX (natural skill, after all, it doesn't cost any mp)... and FFVIII, it's some kind of contract if I'm right.

So, after all I'll stick with Meister on one hand and Coinspinner on the other.