: Add to your mana pool.
, : Add to your mana pool one mana of any color in your commander's color identity. If you spend this mana to cast your commander, it enters the battlefield with a number of additional +1/+1 counters on it equal to the number of times it's been cast from the command zone this game.
10/17/2013 The “number of times it’s been cast from the command zone” includes the most recent time. For example, the first time you cast your commander from the command zone in a game, if you spent mana from Opal Palace’s last ability to do so, it will enter the battlefield with a +1/+1 counter.
10/17/2013 The color identity of your commander is set before the game begins and doesn’t change during the game, even if your commander is in a hidden zone (like the hand or library) or an effect changes your commander’s color.
10/17/2013 If your commander is a card like Kozilek, Butcher of Truth that has no colors in its color identity, Opal Palace’s last ability produces no mana.
10/17/2013 In formats other than Commander, Opal Palace’s last ability produces no mana.