Fit heavy-duty stand mixer with flat beater attachment. Crumble almond paste into large mixer bowl; add 3 cups powdered sugar. Beat on low speed until mixture is crumbly and resembles cornmeal. Add corn syrup and 1 tablespoon water. Mix on low speed, adding additional water, 1 teaspoon at a time, until mixture starts to form a dough. Remove about 1/8 of marzipan for daisies; wrap in plastic wrap and set aside. Add green food color and water, 1 teaspoon at a time, to remaining marzipan; beat on low speed until pale green and consistency of modeling clay. Sprinkle work surface generously with powdered sugar. Knead green marzipan until smooth and color is even, sprinkling with additional powdered sugar as needed to reduce stickiness. Flatten into round disc, about 6 inches in diameter. Double wrap disc in plastic wrap. Refrigerate marzipan at least 24 hours or up to 1 week.