I think the best place for insight into Magic color philosophy is probably Ravnica and its guilds. That shows you a how the colors combine in various ways, and I think that tells us more about the colors than looking at them in isolation.
Azorius Senate – White/Blue. The epitome of order and the codification of law, both as a concept in service to order and as a field of study and knowledge.
House Dimir – Blue/Black. An organization of spies that trade in secret knowledge, and which employs psychic magic to literally rip secrets from your head and feed on them.
Cult of Rakdos – Black/Red. A combination of a religion and a circus, founded on the idea that in the face of a decaying world hedonistic pleasure is the only thing that makes sense.
Gruul Clans – Red/Green. A loose collection of clans who wish to see the world restored to its primal state.
Selesnya Conclave – Green/White. Hippies seeking communion with the World Soul, and desiring a world of harmony between their ordered version of nature and all its inhabitants.
Boros Legion – Red/White. Religious zealots seeking to forge a just society and root out corruption and lawlessness.
Orzhov Syndicate – White/Black. An organization combining the traits of the Mafia and a church, where people fall into debt and need to spend their afterlives in service to the syndicate.
Golgari Swarm – Black/Green. The circle of life, or perhaps of death. Life growing from that which is dead and rotting.
Simic Combine – Green/Blue. Biological monstrosities, seeking to combine and alter life forms into strange and wondrous hybrids.
Izzet League – Blue/Red. The lust for experimentation, crafting ever more dangerous tools and forcing elements into new shapes.
If I were to boil these down into a single trait each, they would be:
White: Order
Blue: Knowledge
Black: Death (this is the one that's most iffy)
Red: Passion
Green: Life
So Green + White becomes a cult dedicated to things living in harmony, Green + Black becomes the cycle of life and death, and White + Black becomes a Church using the forces of order to enforce service beyond death.
These things really don't match very well with D&D classes at all. I think Ravnica had the right tack on it, where you had multiple classes in each guild, just seen through that guild's lens.
Azorius Senate – White/Blue. The epitome of order and the codification of law, both as a concept in service to order and as a field of study and knowledge.
House Dimir – Blue/Black. An organization of spies that trade in secret knowledge, and which employs psychic magic to literally rip secrets from your head and feed on them.
Cult of Rakdos – Black/Red. A combination of a religion and a circus, founded on the idea that in the face of a decaying world hedonistic pleasure is the only thing that makes sense.
Gruul Clans – Red/Green. A loose collection of clans who wish to see the world restored to its primal state.
Selesnya Conclave – Green/White. Hippies seeking communion with the World Soul, and desiring a world of harmony between their ordered version of nature and all its inhabitants.
Boros Legion – Red/White. Religious zealots seeking to forge a just society and root out corruption and lawlessness.
Orzhov Syndicate – White/Black. An organization combining the traits of the Mafia and a church, where people fall into debt and need to spend their afterlives in service to the syndicate.
Golgari Swarm – Black/Green. The circle of life, or perhaps of death. Life growing from that which is dead and rotting.
Simic Combine – Green/Blue. Biological monstrosities, seeking to combine and alter life forms into strange and wondrous hybrids.
Izzet League – Blue/Red. The lust for experimentation, crafting ever more dangerous tools and forcing elements into new shapes.
If I were to boil these down into a single trait each, they would be:
White: Order
Blue: Knowledge
Black: Death (this is the one that's most iffy)
Red: Passion
Green: Life
So Green + White becomes a cult dedicated to things living in harmony, Green + Black becomes the cycle of life and death, and White + Black becomes a Church using the forces of order to enforce service beyond death.
These things really don't match very well with D&D classes at all. I think Ravnica had the right tack on it, where you had multiple classes in each guild, just seen through that guild's lens.