Community

In theory:

White is the color of law and order. It will not doubt to take action, but only if it finds you threatening. Black is the color of selfishness and invidualism, and so doesn't care who you are. If you stand in its way, it's going to kill you, even if it has to pull some convoluted demonic pacts or whatever. It gets the job done.

In practice:

A -White gets Auras that stop a creature, most often from attacking and blocking, but other times from activating abilities as well. However, white doesn't kill them, so their static and triggered abilities still work, and destroying the enchantment leaves the creature free. Examples: Pacifism , Arrest , Faith's Fetters , Bonds of Faith , Burden of Guilt , Recumbent Bliss .

B -White gets Oblivion Ring-like permanents that exile and give it back if the ever leave the battlefield (with the known trick that if you make the permanent leave in response you never give it back). These often don't have restrictions, because the drawback is the possibility to reverse it. However, if it's an enchantment, everyone knows it doesn't really come back that often and against black and red it's like it didn't have any drawback at all. Examples: Fiend Hunter , Oblivion Ring , Journey to Nowhere , Detention Sphere .

C -White gets destruction or exile effects without the possibility of reversing, but they often have restrictions. The most common are checking if a creature is attacking, or if it has an enemy color, but all sort of restrictions can be possible, most often hinting that the creature is somehow dangerous to white. Examples: Avenging Arrow , Divine Verdict , Rebuke , Smite the Monstrous , Celestial Purge , Condemn .

D -White very rarely gets destruction or exile effects that are unconditional and irreversible. The cheaper ones are well known because they are very efficient. Path to Exile , Swords to Plowshares , Afterlife , Oblation . But this also happens with less known cards ("limited fodder") like Iona's Judgment and Trostani's Judgment . The idea is that white gets rid of anything if it gives you something back. This is a bit of a weak argument, and some people inside R&D don't support it, including Mark Rosewater.

E -Black gets direct removal without asking questions, and some that are pretty much unconditional (because the condition is very wide). Murder , Launch Party , Sever the Bloodline , Chill to the Bone , Rend Flesh , Victim of Night .

F- Since black gets so much removal (mostly destruction), the vast majority more efficient but restrictive ones. Doom Blade , Go for the Throat , Ultimate Price , Assassinate . It's impossible that these don't exist, because the design space for unconditional removal is pretty low.

F -Black gets "weaken" -N/-N effects at all sizes and rarities. Examples: Disfigure , Dead Weight , Grasp of Darkness , Death Wind .

G- Black gets "edict" effects, very rarely for all types of permanents. Examples: Geth's Verdict , Liliana of the Veil , Tribute to Hunger .

Conclusion:

A's are very rare nowadays, because B's are the new thing they seem to be exploring a lot. In both cases, though, and except for Fiend Hunter , they are all enchantmens, meaning their possibility of reverting them is just theoretical. The very high-profile D's don't help either.

They used black to explore the many possibilities of removal including conditional ones, so there are a lot of F's, and all the excessive "nonblack" clauses they used in the past don't help.

In the end, I think white is pretty much seen as the best removal color, and black supports that. And not only because it historically has Swords to Plowshares , but because in black you are thinking when to use Doom Blade and when to use Go for the Throat while white very casually just gets Journey to Nowhere , for example.

My solution:

Promote unconditional removal in black. I know it's hard to do so without eating up design space quickly, but they should try.

"Destroy target creature."
"Exile target creature."
"Destroy target creature. Its controller loses 2 life."
"Destroy target creature. Its controller discards a card." 
"Destroy target creature and target land."

are all fine lines for removal spells. If you want to combine it with the set's mechanics, you can have:

", Sacrifice Executioner's Capsule : Destroy target creature."
"... Remove three quest counters from ~ and sacrifice it: Destroy up to two target creatures."
"Destroy target creature. Flashback ."
"Whenever ~ attacks, if you control no other creatures, destroy target creature defending player controls."

And so on. As for white, either make more creatures for Oblivion Ring effects (it's cool because they can have varying stats, costs and abilities) so that the reversible part is present, or just add the same conditions you use in C's.

Criminals' Prison
Enchantment (U)
Flash (You may cast this spell anytime you could cast an instant.)
When CARDNAME enters the battlefield, exile target creature that dealt damage to you this turn.
When CARDNAME leaves the battlefield, return the exiled card to the battlefield under its owner's control.

Trip to Somewhere Nice
Enchantment (C)
When CARDNAME enters the battlefield, exile target nonwhite creature.
When CARDNAME leaves the battlefield, return the exiled card to the battlefield under its owner's control.

That's my input. I'd like to hear opinions on this. 

Today a Gatecrash card was spoiled that makes a Sword to Plowshares for each opponent when it enters.

By R&D's rules white removal is supposed to only work
1: Reactively
2: Be reversable

things like  Trostani's Judgement and  Iona's Judgement violate this.
Being really overcosted does not excuse this.

I hate them so much.

Edit: Forgot about
3: Give something in return (Path giving a land, Swords giving life, Wrath effects being symmetrical), but these have to be costed as such that the trade is 'fair'
The Primordial is fair because its really expensive.
Swords isn't because its instant and only one mana.  

I'm willing to consider sweeps in that last category because they're symmetrical.

Black deals with enchantments and artifacts by Discarding   them or Extracting   them.

Black doesn't get removal for them because it can't destroy things that aren't alive.