Level bottoms of cake, trimming off extra with knife and set on cooling grid positioned over parchment paper.
Tint portions of ready-to-use decorating icing red and green. Heat icing in microwave. Pour one color at a time and tap gently on counter to evenly cover sides. Let dry.
Use tip 5 with white or tinted blue ready-to-use decorator icing, pipe snowflake designs on top of cake. Let icing set. Brush silver pearl dust on white snowflakes and white pearl dust on light blue snowflakes.