Divide corn syrup between two bowls. Tint one bowl with red food coloring to a deep shade, and tint the other with green. Stir half of the melted chocolate coating into each bowl, stirring just until blended. Spread each on a sheet of waxed paper to 1/3-in. thickness (about a 4-in. square). Let stand, uncovered, at room temperature for 2-3 hours or until dry to the touch. Remove clay from waxed paper and gather into a ball. Wrap tightly in plastic wrap, let stand overnight. Use immediately or store for up to 2 weeks.
To make cake top poinsettia: To cut out each leaf or petal, knead a portion of the appropriate color clay until pliable but not soft. Roll clay between sheets of waxed paper to 1/8-in. thickness. Trace the patterns onto another piece of waxed paper and cut out. Place patterns on rolled-out clay and use sharp knife to cut around edge of patterns.
For bottom leaves, cut out three large leaves from rolled-out green clay. Set aside remainder. With the point of a knife, score the veins in the leaves as shown on pattern but do not cut all the way through. Place the large leaves centered on top of the cake with center points touching.
For the bottom flower petals, cut out five large flower petals from rolled-out clay. Set aside remainder. With the point of a knife, add veins as done with bottom leaves. Curve the point of each petal up and shape as shown in photo. Matching centers, place three petals over the leaves, positioning them evenly around and adding a 1/4-in. ball of red clay under the larger curves of petals.
For the top flower petals, cut out three small flower petals from the rolled-out red clay, rolling out additional clay as needed. With the point of a knife, add veins as done with bottom leaves. Curve the point of the petal up and shape as shown. Matching centers over centers of bottom petals, add the top petals between the bottom petals evenly around the top.
For flower stamens, form 3/8-in. balls of green clay. Place several in center of flower, covering all petal centers.
To decorate the sides of the cake: For side leaves, cut out 14 small leaves from rolled-out green clay. With the point of a knife, add veins as done with bottom leaves. Form leaves into seven sets of two leaves each, making centers match and sides overlap as shown in photo. Place sets evenly around the base of cake. Make a small (1/4-in.) ball of red clay and press onto the point where the leaves meet.
To decorate cake sides with additional flowers (as shown on front cover): Cut out 15 additional small flower petals from rolled-out clay. With the point of a knife, add veins as done with bottom leaves. Curve and shape as show in cover photo. For each side flower, form a group of three small petals, bring centers together and overlapping edges as show on cover. Set aside.
Cut out five small leaves from rolled-out green clay. With the point of a knife, add veins as done with bottom leaves. Add one small leaf to the group of three petals and position on the side of cake. Repeat with remaining petals and leaves, forming five side flower groupings around the base of the cake. Add flour stamens, forming several 1/4-in. balls to add to the center of each flower.