Beat together the cake mix, eggs, and vegetable oil just until combined.
Add the food coloring and beat until well mixed.
Stir in the M&Ms and chocolate chips.
Cover and chill for at least 30 minutes.
When ready to bake, preheat the oven to 350 degrees and line a baking sheet with parchment paper.
Use a tablespoon (or a 1 tablespoon cookie dough scoop) to scoop a heaping spoonful of dough. Roll the dough into a ball and place it on the lined baking sheet. Press the dough down slightly, then decorating with additional candy and chocolate chips if desired. Repeat until all the dough has been used.
Bake the cookies in the preheated oven for 10 to 12 minutes, until the cookies are set and the edges of the cookies are just turning slightly golden in color.
Allow the cookies to cool on the baking sheet for 5 minutes, then transfer to a wire cooling rack to cool completely before serving.