can you further explain how they work as this sounds interesting?
Sure.
This site mostly cover the basic ideas:
Final Fantasy XII magicks
(In the case of FFXII, what we usually see as ''red magick'' are split into Time and Arcane magicks. )
Green: Shield, Globe of invulnerability, resilient sphere, absord element, sleep, silence, blind, Augment Abilities, grease.
Red: Haste, Slow, expeditious retreat, elemental weapon, magic weapon, mirror image, confusion, mislead, enervation, disintegration.
Black: Burning hands, fireball, lightning bolt, cone of cold, gust of wind, tsunami, whirlwind.
White: Cure wounds, dawn, restoration, regeneration, raise dead.
Others:
Blue: gain monsters traits from the MM or innate spells in a way resembling the warlock's Invocations.
Geomancer/Animist: A weird one. Imagine a Land druid (druid spell list + varying spell list depending on the terrain), using bard instrument as focus, + the ranger's favored terrain trait.
Astromancer/Oracle: Closer to a Diviner + Divine soul sorcerer. Oracles have more Radiant-blasting spells.
Summoner: Pet-class and summon spells.