Is it impossible to pay off-color mana costs in EDH?

Question

In Commander, there is a rule that states:

• During the game, if mana would be added to your mana pool that isn't a color in your commander's color identity, that much colorless mana is added to your mana pool instead.

With that in mind, is it impossible for me to pay mana costs that are not in my commander's color identity?

For example, if my commander has a Red/Blue color identity, and I take control of an opponent's creature that has an activated ability with a Black mana-cost, is it impossible for me to pay the cost needed to activate that ability?

Answer 1

Yes, it is unfortunately impossible to add mana of a color outside your deck's color identity to your mana pool. Tradtionally this will be mean you cannot pay the cost of this - however, as @AlexP and @Stephen highlight, replacement effects may mean you can activate the ability without adding that color mana to your mana pool.

The comprehensive rules state:

903.9. If mana would be added to a player's mana pool of a color that isn't in the color identity of that player's commander, that amount of colorless mana is added to that player's mana pool instead.

Thus, you can in no way get mana into your mana pool that is not in your general's color identity (which would be required to activate that ability, by using up that mana in your mana pool).

If you can find a way to reduce, alter, or otherwise pay this cost (without adding off-identity mana to your mana pool), it may still be possible to activate the ability - for details, see the answers provided by @AlexP and @Stephen.

Answer 2

It's impossible to add off-color mana to your mana pool. That means that, short of replacement effects that alter how mana can be spent, it's impossible to pay off-color mana costs.

So, what do those replacement effects look like? Cards like Mycosynth Lattice allow you to spend mana "as if it were any color of mana" without actually changing the colors of that mana.

There's a really technical caveat to that, though...

I'm pretty sure that, even with Mycosynth Lattice in play, there are still corner cases where mana colors matter: for instance, Mycosynth Lattice will allow me to spend 5 blue to cast Torrent of Souls, but the spell still checks the color of mana spent on it (which, in this case, causes it to have no effect). This is based on the rulings text of Celestial Dawn:

You may use a different color mana than the color required for spells and abilities that require a specific color. If you do, and the spell or ability checks the actual color of the mana, it can tell the difference.

Answer 3

You may use Mycosynth Lattice, as Alex P stated, to pay the activation cost even though the mana colour is not in your colour profile. Here is why:

Let's assume I have a Mycosynth Lattice in play and in some manner I gain control of a creature that has an ability not in my commander's colour profile.

Using conventional means I cannot pay this cost since I cannot generate any coloured mana in my mana pool that isn't a colour in my commander's colour profile by 903.9.

The Lattice doesn't say add any colour to my mana pool, it reads as a replacement effect and says that I can spend mana as though it were of any colour.

This to means that if I had a red mana in my colour profile but not black, I could tap a mountain to pay B on a creature's activated ability since I am adding R to my mana pool but spending it as though it were B.

This argument satisfies 903.9's requirements but still allows the ability to be paid, confirmed by a Level 1 DCI Judge at this link.