I was in a multiplayer and I observed this situation- my buddy played {Moltensteel Dragon} which requires 4 and either 2 red or 4 life. He used 5 red mana and 2 life. My other buddy pulled a counter red or green spell. I forget the card but he retracted his action cause he thought it was colorless because it's a artifact creature. I said he did use red mana to summon it. So my question is if you have an phyrexian artifact creature that requires either life or red mana and you use red mana for the cost, does it make the creature a red spell
Even if you paid 4 colorless and 4 life, the spell is still red. Paying 2 life for Phyrexian mana produces the color of mana needed, in this case red mana. A card is always the color or colors on the card, take {unmake} for example, you could use 3 black to cast it but it will still be a white and black spell.