Line an 8×8-inch pan with foil and spray with nonstick spray.
In a medium microwave-safe bowl, combine the white chocolate bars, sweetened condensed milk, and butter. Microwave on high for 1 minute, then stir. Continue microwaving in 30-second bursts, stirring each time, until smooth and creamy.
Stir in the orange extract. Taste and add more if needed.
Remove 2 cups of the mixture and place it in a separate bowl. Leave this portion white.
Add the orange food coloring to the remaining mixture until the desired orange color is reached.
Pour the orange fudge into the prepared pan and smooth it out evenly.
Drop the white fudge over the orange layer by spoonfuls in a random pattern.
Use a knife or wooden skewer to swirl the two colors together.
Tap the pan on the counter a few times to remove air bubbles. Pop any large bubbles with a toothpick if needed.
Refrigerate uncovered for 4 to 5 hours, or until fully set.
Remove the fudge from the pan, peel back the foil, and cut into squares before serving.