If you do not know, there is a system of 5 colors in Magic the gathering.
Green, blue, black, red, and white.
Green is nature, blue is magic and intelligence and stuff, black is death, red is fire and chaos, and white is light and peace.
So find a hero, and find their colors!
You just opened a whole can of nerd, my friend.
Should be stated that someone’s colors can drastically change between moments in time depending on their mood and state of mind, it’s a pretty flexible (and sloppy) system.
Here’s an almost bare bones explanations of the colors:
Red is depicted as fire and chaos in-game because that’s what you’re going to see in most battles, but it’s explicitly clear it’s mainly the color of all things intense and passionate, whether it’s love or hate, pain or ecstasy. Also the usual color for hot heads and loose cannons. 
White is primarily order, community and perseverance. Justice and(/or) Law being upheld no matter what moral grey areas it might circumvent in the process. Very much representative of holy powers (The Light) and healing.
Green is the simplicity of the natural order. The law of the jungle and cycle of life and so on. It’s the color mainly used to represent beasts and other creatures that are true to their instincts or some other primal direction. Shares a lot of similarities with white when regarding community and healing.
Blue is intelligence. Creative thinking and adaptability, often detached from emotion in favor of progress. That, or willing to forgo tradition or “common sense” in favor of their own rationality. Of course it’s also the color for water and ice.
Black is power above all else, pure ego. Overcoming any obstacle, crossing every line, and taking whatever you please, no matter the sacrifices. Very much the color of necromancy and other dark arts. Often used for poison, alongside Green.
Most complex characters are prone to having several colors and color changes over time, so I’ll try to list their colors in order of importance though it might be pretty split for some of them.
Garrosh - Red
Gul’dan - Black
Varian- White/Red
Thrall - Green, White, Blue
Alexstraza - Red, White
Medivh- Blue, White
Malfurion- Green
Tyrande- Green
Zul’jin- Green/Red
Rexxar - Green
Lich King - Black
Arthas - White, Red, and later on Black
Kel’Thuzad - Black/Blue
Anub’arak - Black, perhaps green
ETC - Red
Artanis - White, Red
Tassadar - White, Blue
Raynor- White, a splash of blue
Tychus- Red
Dehaka- Green
Abathur- Blue/Green
Kerrigan- Black early on, Red later, Green
Zagara- Green
Blaze- Red
Imperius- Red/White
Tyrael- White
Johanna- White
Kharazim- White
Nazeebo- Black, Green
Leoric- Black, White
Butcher- Red/Black
Diablo - Red
Mephisto - Black, maybe Red
Azmodan - Red, Black
It’s usually pretty cut and dry.
Some ones I’m having difficulty placing though:
Brightwing - Red?
Stukov - Red and Green? White?
Green/red
Black/green?
I’d say Brightwing is green/red.
Stukov, we don’t really know his motivations at that point so, anyone’s guess. But since he stayed with the swarm. I’d say green for now.
Also, I’ll add that white is very much about the group over the individual, and black about the individual before the group. Which is why they don’t tend to get along outside of stuff like Orzhov (Who betray each other anyway).
White color combos are always great, it’s duality at it’s finest.
Red/White/Black has always been my favorite tri-color combo because of how hard those ideologies clash with each other and what it says for the kind of person who can only be represented by all of them at once.
I’ve always been a fan of white/black or black/blue.
green/blue is the weirdest because even the designers have a hard time finding stuff that fits it without simply mashing tow things from each color.
And red/blue always ends up clashing so much that the card it gets are inconsistent.
Color combinations were a tricky thing for them to figure out at first but Ravnica set a very strong precedent. They’re still an overall mess that settled into certain niches but things just get so convoluted when there’s more than 2 colors involved.
I wish the game didn’t turn out the way it did. Each new spoiler season drains away my soul as every card is a self reliant value engine with multiple other abilities stapled on.
Starts as just a soldier (most likely red).
Then becomes possesed by amon (effectively no self control), because she cant control it, i would still say this is red again.
Once freed from amon (and human again), starts to flee from becoming a test subject, This surely is ego, but at the same time also a lot based on emotion, so i would say this is black/red, with a tint of green (although she gives that role to abathur/zagara etc). Especialy since she wants to rescue raynor i would say red becomes quite dominating.
Once that phase is done, and she is the zerg queen again, she starts to take it against amon in an act of justice. And at this phase i would then say white/green.
I dont know the story before she was converted to the zerg queen, but i would not expect that to be black as she seems very emotion driven.
Alarak - Black
Hogger - Red
Deathwing - Red
Whitemane - White/Black
Deckard - Blue
Murky - Colourless
Mal’ganis - Black
Imperius - The Whitest White that has ever Whited
Illidan - Green/Black
Tassadar - White
Garrosh - Red/Black
Probius - Artifact
Greymane - Red
Lunara - Green
Anduin - White
Ana - Blue
Malthael - White/Blue/Black
Zarya- Red
Zeratul - Blue
Mei - Blue
Xul - Black
White-Red.
Nah. I think Red fits his personality, but the evil side of White is all about purity. Imperius is so about purity, that I think it overrides the Red part.
Plus, he’s an angel. That’s like 50,000 extra White points.
Imperius is definitely not white, he is somewhat the opposite of tyrael on that. I would instead say that blue would be even more likely visible than white. Since although its moraly not justified, it is wise to consider humans as a problem. Thats a statement white would not make.
I think imperius is just pure red.
I say red as he is very militant
Well. I’m sure they would do things very differently if they had to start over.
They actually did duel masters, which had the best system ever. It was pretty much a fixed MtG. But people didn’t like it because, it wasn’t MtG.
But WotC never re-used the mana system in any game ever again. That says a lot.
Any DM card could be played upside down as ressource.
Church militant falls under White, and there’s rarely a warrior more holy than Imperius.
I think it’s debatable. I think that in Imperius’ mind, he’s mono-White. That’s the version I was seeing.
I’m also trying to avoid multi-colours as much as possible. Slapping multi-colours on every hero is a pretty easy trap to fall into. I think it’s more interesting to find the one colour that fits.
The issue is that holy in diablo doesnt work the same as in magic. In diablo you therefor generaly speak about humans, angels and demons, as if they are factions.
This means that even angels can be evil (as malthael shows), yet technicaly not directly being evil. Malthael only wants to kill humans because they are a vessel for evil to reach angels. Taking out humans protects the angels.
This is more an act of blue than black. Its just that he uses a black act for that part. But he might just use that for the blue purpose, as maybe for him humans are just a disease that need to be cured.
Also, angels even have their own religion with their own sacred parts. They might be holy to humans, but to themselve, they are just angels. Being holy is the status of the crystal arch from the standpoint of angels.
If humans would even know how angels work (which they dont), they wouldnt even consider them holy anymore. They would be a threat as much as demons. As both have very good reasons to abuse them for their own benefits.
Angels however do more often show the white aspect, while demons nearly always show black (but note, black is not mandatory! demons can just be a slave of an other demon, making them mostly red instead of black again).
White should not be seen as holy in the diablo universe, it should be seen as unity here. The opposite of ego. You do not want to take out a group, just to protect yourself, as thats a sign of ego. Yet this is what imperius wanted to do towards humans (and tyrael just convinced him not to), and what malthael was trying to do.
I’m not going that deep with it. I was just going with what they’d be printed as if they were MtG cards.
Probius: mono blue (I can already imagine some kind of card draw that makes you win the long value game)
Tychus: tychus is upfront on offence but lacks the up in your face that boros represents. I’d say he’s mono red.
Brightwing: definitely symic. Versatile and packing so much utility is simic’s brand. Plus I see her global as a sort of ramp.
Anduin: mono white. I thought of Azorius but Anduin is more of a “we stand together” than a person seeking justice. Which brings me to…
Tyreal: Azorius I mean come on.
Imperius: pure boros I mean come on
Uhhh who else.
Malthael: Black/White/Blue
Mephisto: Black/Blue
Auriel: Mono white
Sonya: Mono red
I’d say Mephisto is more like rakdos. Dimir is a lot less offensive than it is more on the oppressive.
Malthael might be more mono black but it’s also a good argument that he’s esper.
Gazlowe is Izzet because gadgets and also he’s the inventive type, not mad sciency though but enough tinkering to be under these colors.