Prepare the Pan: Line an 8x8 inch pan with parchment paper, ensuring it hangs over the edges for easy removal later.
Mix the Green Layer: In a bowl, combine 1 can (14 oz) of sweetened condensed milk with 4 drops of neon green food coloring and mix well until evenly colored.
Melt the Ingredients: In a medium pot, combine 3 cups of white chocolate chips, the green sweetened condensed milk (from the previous step), and 4 tbsp of unsalted butter. Heat over low to medium heat, stirring constantly until melted and smooth. Stir in 2 tsp of green apple extract until incorporated.
Pour the Green Mixture: Carefully pour the green mixture into the lined pan, spreading it evenly. Let it sit at room temperature to harden overnight.
Prepare the Black Layer: Repeat the melting process using another 3 cups of white chocolate chips, 1 can (14 oz) of sweetened condensed milk, and 4 tbsp of butter. This time, add 4 drops of black gel food coloring and stir until the chocolate melts and the color is uniform. Stir in 2 tsp of green apple extract to maintain the flavor consistency.
Add to the Pan: Once the black mixture is ready, pour half of it over the hardened green layer, pressing it gently to create a seal. Pour the remaining black fudge on top, ensuring it covers the entire surface.
Final Hardening: Allow the fudge to harden in the refrigerator overnight. Once completely set, use the parchment paper to lift the fudge out of the pan and cut it into squares.