It's not that simple...

Chose a color. Extrapolate how many cards of
that color a targe opponent has in his hand. That opponent then reveals their hand. Until the end
of the turn, you may cast an instant or a sorcery
spell with converted mana cost {x} from your
hand without paying its mana cost, where {x} is
equal to the number you extrapolated minus the difference between the number you chose and
the number of cards of the chosen color.
Draw a card.