Temper the Veil

As you cast Temper the Veil, you may choose to
cast it without color.
If this spell is colorless as you cast it, creatures
your opponents control get -2/-0 until end of
turn, then those players discard a card.
If this spell had one or more colors as you cast
it, creatures you control get +2/+0 until end of
turn, then draw a card