Melt the butter and marshmallows in a microwave safe bowl, heating in 30 second increments and stirring in between. My microwave only needs one 30 second burst.
Add the food coloring gradually and stop when you reach the desired color.
Mix in your Rice Krispies and stir to coat them completely in the butter-marshmallow mixture.
Press your Rice Krispies mixture into a prepared heart-shaped pan, or heart-shaped muffin liners. If using a metal pan, I like to give it a generous spray with PAM.
Place in the fridge and allow to set up to one hour before serving.