Line an 8X8 pan with parchment paper or wax paper and grease with butter.
Add 2 1/2 cups white chocolate chips plus the milk chocolate chips and sweetened condensed milk to a microwave-safe bowl. Put in the microwave for 30 seconds. Stir, then repeat in 15-second spurts. Stir between each one. Do this until melted.
Add in the red food coloring.
Pour the fudge mixture into the pan and put it in the fridge for 2 hours.