You must use paste food color to achieve the bright red and blue colors. If you use liquid or gel food color, your cake color will be pastel.
Find paste food color at large craft stores.
Don’t have a 4-inch round biscuit cutter? Cut out a 4-inch circle of cooking parchment paper, and use it as a pattern.
To easily cut cake layer horizontally to make 2 thin layers, mark side of cake with toothpicks and cut with long, thin serrated knife.