So I'm jus curious what plane these creatures are implied to be from:
Alabaster Mage
Azure Mage
Onyx Mage
Crimson Mage
Jade Mage

Are they from Shandalar (as they debuted in a core set) or simple, vague multiversal concepts? My headcanon overall is that these descriptions are more elegant titles for spellcasters with no better description of their magic, or perhaps a simpler slang-ish title for more specific mages in idle conversation ("Watch out for that crimson mage over there, he's likely to cause a fiery mess. Oh. Pyromancy is his only magical talent") and sort of fills in for a more Magic-sounding color-magic title for mages, a la Final Fantasy or even more traditional fantasy, for example I imagine in MTG, Gandalf would be dubbed "Gandalf the Alabaster". Though I get the feeling the titles only apply on worlds where spellcasters strictly understand the differences in mana and categorize types of magic as such. I don't see a Thaumaturge of Thassa to be dubbed an Azure Mage by a denizen of Theros, for example.

Because of the specific, quoted, and named creeds of the five flavor texts, I get the feeling that they are specific. Crimson Mage is clearly a pyromancer, and has 's stereotypical attitude toward war and rage, and so could be archetypal, but the fact that they gave him specific words and labeled them "Crimson Creed" tells me it is reflective of a specific culture, perhaps even a religion, that would be inherent to one plane rather than a general, any-plane pyromancer.

I do know they feel laughably stereotypical and make me want to write better flavour texts.

Except for the one. It's cool. Literally.

What Raven said.
I like to think that they could be members of the magic guilds on Shandalar, if those still exist. The guilds were specifically mono-colour focused after all.

Oh. Nice. Shandalar is definitely a plane I hope receives a standard block and thus revisiting flavor and such.

The White one has awesome flavor text too. Nobody expects a good flavor text in core sets...
PAAAAAAAM !!!!!
"Truth and honor are our greatest weapons! And surprise ! And ruthless inquiry ! And fanatical devotion to Pope !"