With the takeover of the plane of Mirrodin by the Phyrexians we are introduced to a new way to cast some spells and pay for some abilities. There are a total of 26 cards in New Phyrexia that have a Phyrexian mana symbol in either the mana cost of the card, as a cost to play an activated ability, or both.
The Phyrexian mana symbols are symbol for Phyrexia (the rough circle with a line though) with a background that is one of the five colors of Magic. These symbols only appear in the costs of spells and activated abilities. This cost can be paid by either paying the normal mana of the appropriate color or by paying 2 life. These mana symbols do not represent a new color of mana, they represent a choice. They only appear in costs, so it is not possible to add Phyrexian mana to your mana pool.
When casting a spell or playing an ability with a Phyrexian mana symbol you choose for each of these mana symbols how you will pay. For example, when casting Dismember you can either pay 1BB, 1B and two life or 1 and four life. As mentioned you make this choice when you announce the spell or ability and put it on the stack.
Regardless of how you do actually pay for these spells, their converted mana cost remains the same. For example, the converted mana cost of a Moltensteel Dragon is six, it does not matter if any life was paid when the spell was cast. Similarly, the option of paying life instead of mana does not change the color of the card, spell or permanent. Apostle’s Blessing is a white card regardless how it was paid for.
Finally, as mentioned in the tip yesterday, you cannot pay life if an effect prevents your life total from changing. Similarly, you cannot pay the two life if your life total is one or below.