Prepare cake batter with noted modifications (or not, whatever suits you), mix with an electric mixer or electric beaters. Stir in chocolate chips, if using.
Spray bundt pan with cake release, and bake according to package instructions.
While cake is baking, put icing in a bowl and whisk milk into it until you reach a pourable “slime” consistency.
Divide icing equally into small bowls - use a bowl for each color you will be using. Add food coloring to each bowl, whisk until incorporated, and set aside.
When cake is done baking, remove from pan and allow to cool completely. Pour icing over top, then add sprinkles.