Line an 8x8 pan with tin foil making sure to have the foil hanging over the edges (for easier fudge removal). Coat the tin foil lightly with cooking spray.
In a small sauce pan, over low heat, melt the white chocolate chips.
In a separate sauce pan, over low heat, melt the milk chocolate chips.
Add half of the sweetened condensed milk to the melted white chocolate chips and the other half to the melted milk chocolate chips.
Remove the pans from the heat and stir both pans until they are fully melted and well combined.
Add the mint extract and the green food coloring to the white chocolate chips; stir until fully combined.
Working quickly, drop a few spoonfuls at a time of each one into the foil lined baking pan. Continue adding randomly until both sauce pans are empty.
Shake the 8x8 pan a little to make it even and tap it firmly on the counter to remove air bubbles.
Very gently run a butter knife or wooden skewer through the batter a few times to give it a swirled effect.
Place into the refrigerator for at least two hours.
Remove from the refrigerator and pull the hanging edges of the tin foil (with the fudge) out of the pan and away from the fudge.
Cut into small square pieces - a little goes a long way! Enjoy.
Store in the refrigerator in an airtight container.