Can a commander deck use abilities of creatures or spells, and generate mana that are not part of the commander's color identity? For example, if my commander has only black in its color identity, can I cast Unburial Rites, a black creature, and use the flashback ability which requires white mana? Similarly, can I have lands that produce white mana as part of the deck?
Mostly no, you cannot have cards with a different color identity from your commander in your deck, including your lands. There are however ways to cast off color spells and have off color mana.
Color vs Color Identity
First there's a difference between a card's color and its color identity. The color identity of a card is set by four things:
- The colors in the color indicator on the card
- The colors of the mana symbols in its casting cost
- The colors of any mana symbols in the card's rules text (not reminder text - important for extort1)
- The colors associated with any basic land types that card has.
The card's color cares about only the first two of these things, and about the devoid keyword (identity ignores devoid).
Playing Unburial Rites
You can't have it in your deck unless your commander is both black and white, because the color identity of unburial rites is both black (because of the casting cost) and white (because of the flashback cost).
You can still cast the spell, but it would have to come from your opponent's deck, stolen with something like Gonti, Lord of Luxury or Hedonist's Trove. (You would not be able to flash it back, since it would be in your opponent's graveyard, they could flash it back)
Playing White Producing Lands
Lands that have a basic type don't actually have the tap ability on their rules text (it is reminder text if it is ever printed on them), but they are covered by point 4, so you can't have cards with the plains type in your deck if you aren't playing with a white commander, so that leaves out several land types that produce white mana (basic, shock, triomes, etc).
Lands that can produce any color however don't fall under either of these color identity rules. Land like Exotic Orchard, Mana Confluence or Vivid Marsh could all be played in a black deck and be used to produce white mana3 if you needed it, to play cards stolen from an opponent or to pay into Sunburst(Etched Oracle)/Converge(Painful Truths) mana costs that care about color.
- Extort is a triggered ability that lets you to pay to drain one life from your opponent whenever you cast a spell. However it is a keyword ability and the mana symbols are in the rules for that keyword, not the rules printed on the card, so it does not have any effect on the color identity of cards with extort, Crypt Ghast is playable without white in the commander's identity and Blind Obedience is playable without black in the commander's identity.
- An interesting side note, Urborg, Tomb of Yawgmoth doesn't have the swamp type and doesn't tap for black until it is in play, so it can be in any color of deck (potentially useful if you're planning to exploit swampwalk)
- This was a change to the rules in 2017. Previously any mana you tried to generate outside your commander's colors would come out colorless. The change was made in part due to the addition of the symbol for colorless mana - which meant you could use this color drained mana to pay costs you couldn't have used the colored mana to pay and in part due to the addition of the Converge mechanic at that time, which cared how many different colors were spent to cast the spell.
You cannot have Unburial Rites in your deck at all as it has a colour identity of black and white due to the white in the activated ability. The same applies to the majority of lands which generate white mana - specifically, any land which includes a white mana symbol, either implicitly as in basic Plains or explicitly as in Glacial Fortress is not allowed. (You could have one of the "rainbow lands" which allow you to add any colour of mana, for example City of Brass).
The only way this could work is if you have somehow stolen Unburial Rites from your opponent, but then it will never be in your graveyard so you would never been able to activate its flashback ability.
Any card with a color not in your commander's color identity can't be in your initial deck. That includes not only the casting cost of the card, but any mana symbol on it, including activation and upkeep costs. There are ways of generating mana that aren't in your commander's color identity, such as Chromatic Lantern, and you can spend that mana, but there aren't going to be many cases where there would be any point. For instance, if your commander is Tergrid, God of Fright and you have five lands and Chromatic Lantern out, you can say "I'm tapping two of my lands to produce one black mana each, and three of them to produce one green mana each, and then using that mana to cast Tergrid, God of Fright", but that would be kind of pointless.
Cards that actually call for off-color mana would generally not be allowed in your deck, but there are cases where off-color mana would be useful, such as: you have a card that allows you to cast or otherwise refers to colors on an opponent's cards, you bring in a card from out of the game (depends on house rules whether that's allowed at all, and if so whether it can be off-color), or you have a card that cares about the number of colors of mana (for instance, if you have Radiant Epicure and can produce all five colors of mana, you can have X be 5).