Corrupted Grafstone

Oracle Text

Corrupted Grafstone enters the battlefield tapped.

T: Choose a color of a card in your graveyard. Add one mana of that color.

Card Rulings

4/8/2016 Colorless cards have no color, so you can’t add to your mana pool this way.
4/8/2016 Players can’t respond to mana abilities, so no player can take any action to stop you from getting the color of mana you expect to produce once you announce the ability.