Line small loaf pan with parchment paper and grease.
Place white chocolate chips and sweetened condensed milk in a medium microwave-safe bowl. Microwave at 30-second intervals, stirring in between until chips are thoroughly melted and the sweetened condensed milk is incorporated.
Pour half molten fudge into another microwave-safe bowl and set aside.
To one bowl, add cinnamon, cayenne pepper, and red food coloring. Stir to blend. Add more red color or cayenne as desired.
Pour red spicy fudge into the loaf pan. Tap the pan on the counter to level the top and release air bubbles. Refrigerate until set.
Once the red fudge is set, warm the uncolored half of the fudge by microwaving and stirring as before until fudge is runny.
Add vanilla extract and blue coloring. Stir to blend. Add more blue food coloring until the desired shade is reached.
Pour blue fudge over red and chill until set. The heat from the warm blue fudge should be enough to weld the colors together.
Once fully set, remove fudge from the pan. Cut into strips that are half and half.