Make the cake mixes (in two separate bowls) according to the box directions. Tint one of them with green food coloring, adding as much or as little until desired color is reached.
Grease both loaf pans and pour the green cake batter into one of them. Bake for about 20 to 25 minutes or until a toothpick inserted in the middle, comes out clean. Remove from oven and allow to cool down completely. Cut into 1-inch thick slices and cut out the center with the shamrock cookie cutter.
Pour a little bit of the untinted cake batter into the second greased loaf pan, enough to cover the bottom. Then place the shamrocks, upright, in a straight row down the middle. Pour enough batter over to cover the sides and top of the shamrocks.
Bake for about 15 to 20 minutes or until a toothpick, inserted in the middle comes out clean. Remove from oven and allow to cool down completely before slicing. Cake will keep well wrapped at room temperature for up to 3 days or in the fridge for 5 days.