Single Color Match Bonus: at the end of your turn you may lay one card from your hand face-up in the Center Row.
Double Color Match: at the end of your turn you (1) lay one card from your hand face-up in the Center Row and (2) all other players must draw one card from the Draw Pile.
May I choose not to lay down a card for a Single Color Match? It might be better to end my turn with two cards instead of one, and the word "may" implies a decision; further, the word "may" is absent from the Double Color Match passage of the rules.