In advance: Make fondant hearts. Press fondant into Hearts Candy Mold dusted with cornstarch. Unmold; insert toothpick into bottom, leaving 1 1/2 in. exposed. Let dry 48 hours. Also: Make fondant flowers and leaves.
Make petits fours and
cover with tinted cookie icing. For rose cakes, use buttercream to pipe rows of tip 3 dots, about 1 in. apart, on cake sides. Outline and fill in center heart with tip 3; smooth with fingertip dipped in cornstarch. Pipe tip 2 dots around heart edge. Insert heart on top. For green cakes, attach flowers and leaves with tip 2 dots of buttercream.
*Combine Lemon Yellow with Golden Yellow for yellow shown.