Add the butter and mini marshmallows to a large, microwave-proof bowl. Microwave for about 1-2 minutes, until marshmallows and butter are just melted.
Working quickly, divide the mixture up into 4 bowls (you can use the large bowl you microwaved the mixture in as one) then add your food coloring of choice to each bowl. Stir to distribute the color then add 2 cups of cereal to each bowl and stir until mixture is cohesive. You can also add sprinkles to any of the mixtures at this time, if you’d like as well.
Generously grease your hands with some oil and scoop about 1/4 cup portions of the mixture into your hands, shaping into an egg shape. Set aside on a plate or baking sheet to harden completely. Repeat with the rest of each color of rice crispy treat mixture.