Place the cake in the fridge to chill while you make the whipped cream
Place 1 1/2 tbsp of cold water in a small bowl. Sprinkle the top with gelatin powder. Wait 5 minutes until the gelatin blooms.
Microwave the gelatin for 5 seconds until it melts and there are no more grains. If it's not melted place in microwave for 3 - 5 more seconds.
Add 1 tbsp of whipped cream to the gelatin and mix. If it hardens, place in microwave for another 5 seconds until liquid again.
Place the whipped cream, powdered sugar, and vanilla extract in a large bowl. Use a hand mixer of stand mixer fitted with a whisk attachment, beat on medium speed until soft peaks form. Pour in the gelatin mixture. Whisk on medium-high speed until stiff peaks form. Divide in half and fold in pink dye in one half, and purple dye in the other half.
Place a 1/2 inch closed star tip in a piping bag. Fill one side of the bag with pink whipped cream, and the other side with purple whipped cream.