Magic the Gathering

[Magister Magi]

No, it doesn't. You have to pay 1 mana each time you wish to prevent a source of that color from dealing damage to you.

For example, let's say I have Circle of Protection: Black. My opponent casts Syphon Soul. I pay one mana to negate that damage. Then during the battle phase, they attack me with Vampire Nighthawk. I must pay one more mana to negate that damage.

Basically, you can only use Circle of Protection: 'Insert Color Here' so long as you have the mana to pay for its ability. Of course, that doesn't stop it from being negated when it's cast, or destroyed later on.

If any other Magic players reading this notice that I am wrong, feel free to correct my mistake.