Bake brownies according to package directions in an 8x8-inch pan lined with aluminum foil and sprayed with cooking spray. Let cool.
Using an electric mixer, cream corn syrup, 4 tablespoons butter, and vanilla.
Gradually beat in powdered sugar.
Transfer half of the mixture to a medium bowl. Add yellow food coloring to what's left in the mixing bowl to get it the desired color.
Spread the yellow mixture on top of brownies. Refrigerate 15 minutes.
Spread white mixture on top of yellow mixture. refrigerate 15 minutes.
Combine chopped chocolate, cream, and 1 tablespoon butter in a medium saucepan with a heavy bottom. Heat over medium-low heat, stirring frequently, until chocolate is completely melted. Let cool 5 minutes and then pour oven brownies.
Refrigerate at least 30 minutes before cutting into squares.