Put oven rack in middle position and preheat oven to 350°F. Butter a 13- by 9-inch baking pan and line bottom with wax paper, leaving a 2-inch overhang on 2 ends, then butter paper.
Beat whites in mixer fitted with whisk attachment at medium-high speed until they just hold stiff peaks. Add 1/4 cup sugar a little at a time, beating at high speed until whites hold stiff, slightly glossy peaks. Transfer to another bowl.
Switch to paddle attachment, then beat together almond paste and remaining 3/4 cup sugar until well blended, about 3 minutes. Add margarine (or butter) and beat until pale and fluffy, about 3 minutes. Add yolks and almond extract and beat until combined well, about 2 minutes. Reduce speed to low, then add flour and salt and mix until just combined.
Fold half of egg white mixture into almond mixture to lighten, then fold in remaining whites gently but thoroughly.
Divide batter among 3 bowls. Use a food scale to make sure the batters are even. Leave one bowl plain for the white bowl. Set the white batter bowl aside. Stir red food coloring into one and green food coloring into another. Chill green and white batters, covered. Pour red batter into prepared pan and spread evenly with offset spatula (layer will be about 1/4 inch thick).
Bake red layer 8 to 10 minutes, until just set. (It is important to undercook. They’ll look like they’re not done, but a tester does come out clean.)
Using extra parchment paper overhang as “handles”, transfer layer to a rack to cool, about 15 minutes. Clean pan, then line with parchment or wax paper and butter paper in same manner as above. Bake white layer in prepared pan until just set. As white layer bakes, bring green batter to room temperature. Transfer white layer to a rack. Prepare pan as above, then bake green layer in same manner as before. Transfer to a rack to cool.
When all layers are cool, invert green onto a parchment or wax-paper-lined large baking sheet. Discard paper from layer and spread with half of preserves. Heat up the jam in a a small bowl in the microwave (or in a sauce pan if you don’t have a microwave like me) for one minute to help it to spread easier. Spread half of the jam over the green layer. The jam should be a very thin layer. Invert white on top of green layer, discarding paper. Spread with remaining preserves. Invert red layer on top of white layer and discard wax or parchment paper.
Cover with plastic wrap and weight with a large baking sheet. I placed cookbooks on top of the baking sheet. Chill at least 8 hours.
Remove baking sheet and whatever you used to weigh it down and plastic wrap. Bring layers to room temperature.
Melt chocolate in a double boiler or a metal bowl set over a saucepan of barely simmering water, stirring until smooth. Remove from heat. Keep chocolate over water. (Alternately, you can do what I did: melt the chocolate about 3.5 ounces at a time just to make sure it doesn’t firm up between steps).
Trim edges of assembled layers with a long serrated knife. Quickly spread half of chocolate in a thin layer on top of cake. Chill, uncovered, until chocolate is firm, about 15 minutes. Cover with another sheet of wax paper and place another baking sheet on top, then invert cake onto sheet and remove paper. Quickly spread with remaining chocolate. Chill until firm, about 30 minutes.
With a serrated knife cut the cake into rows, then cut the rows into squares or rectangles. Be sure to use a wet towel to clean knife after each slice. Try to cut while they are still very cold. If you notice the chocolate melting too quickly after first slices, place in the refrigerator again to let it chill some more and then cut again. You could cut into 4 portions or cut into more like I did. I wanted the cookies to be about 1 1/2 inches wide. The cookies should be cut about 3/4 inch wide. If you have the patience and the time, do freeze the cake before slicing. I've done it both ways and it's much easier to slice when frozen.