Analytical Expertise

Polarity 2 (You may pay up to two mana in any
combination of colors in addition to this spell's mana
cost when casting it. If you do, this spell's color
identity becomes each color of mana paid this way.
Otherwise, its identity is colorless.)
Whenever you cast a spell of the same color as
this enchantment, draw cards equal to the
number of colors in this enchantment's color
identity, then discard a card.