if someone has an all white commander like {elesh morn, grand cenobite} can a card like {blind obedience} be in the deck because of the extort's color cost?
Short answer: They can run the card.
Longer Answer: The black/white hybrid symbol used for Extort is in the reminder text, which doesn't factor in to color identity.
That means that anything with an activated ability of a different color cannot be used. Ex. {lingering souls}
Quote from: An Angry Fatman on January 30, 2015, 01:50:34 AM
That means that anything with an activated ability of a different color cannot be used. Ex. {lingering souls}
Anything in the text box that isn't reminder text is counted. This includes alternate/additional costs, activation costs, and mana produced by mana abilities. Lingering Souls has a color identity of BW, since it has B in it's Flashback cost.