Heat the oven to 180°C /350°F.
Use a food processor to blend the almonds and pine-nuts into a "flour".
Beat the eggs until they become thick.
Sieve the all-purpose flour and icing sugar. Add it to the 'nut' flour, and mix.
Add the egg mixture to the dry ingredients, and mix well.
Break the dough into three pieces.
Knead the lemon zest into one ball, the cocoa powder into the second, and the food colouring into the third, until they are evenly coloured.
Roll the dough balls into long sausages.
Line a baking tray with baking paper, then break off bits of dough a little smaller than the size of a walnut and roll them into a ball, then flatten them very slightly. Place them on the baking tray with at least 5 cm/2 in distance between the cookies.
Bake for 10 - 15 minutes until they are slightly browned.
The cookies can keep for a week in an air-tight container.