12 ounces cream cheese, softened
1 tablespoon milk
1 teaspoon vanilla extract
1/4 teaspoon table salt
1 pound powdered sugar
1 cup white chocolate morsels
2/3 cup milk chocolate morsels
1 (1-oz.) bottle red liquid food coloring
1 cup toasted chopped walnuts
Line an 8-inch square pan with parchment paper, extending over sides; coat with cooking spray.
Beat cream cheese and next 3 ingredients with an electric mixer until creamy. Beat in powdered sugar, 1 cup at a time. Beat at high speed 3 minutes.
Melt white chocolate according to package directions; beat into cream cheese mixture. Reserve one-third of cream cheese mixture. Melt milk chocolate according to package directions. Stir milk chocolate and food coloring into remaining two-thirds of cream cheese mixture. Fold in walnuts. Pour into prepared pan; tap pan on counter to remove air bubbles. Freeze 10 minutes.
Spread reserved cream cheese mixture over fudge; chill 4 to 24 hours. Remove fudge from pan. Cut into rectangles, rinsing and wiping knife clean between each slice. Chill until ready to serve.