In the bowl of an electric mixer, add the almond paste and beat just to break up the almond paste some. Add about 1 cup of the sugar and mix until it is incorporated. Add the remaining sugar and beat until incorporated. The mixture will look like coarse bread crumbs at this point. Add the corn syrup and mix to combine well. The mixture will still be very crumbly.
Turn the mixture out onto a clean work surface and knead until it makes a smooth dough. If the dough seems too sticky, knead in a little more confectioners' sugar. The dough can be tightly wrapped and refrigerated at this point. If you want to color the marzipan, break off the amount of dough you want colored. Add a drop and knead in. For more intense color, add more food coloring. Shape into desired shapes.