Preheat the oven at 180*C / 350*F as instructions given on the cake box. Line a cookie sheet with parchment/butter paper and set aside.
Take a large mixing bowl. Empty the cake mix into the bowl and as per instructions add water+oil+eggs to the bowl. If you want to skip the eggs then use 3/4 cup of thick yogurt for the same, as I did and it came out well. Mix all the ingredients well for 2 minutes with a whisk or electric beater.
Divide the cake batter into 2 equal parts, almost 2 cups each. Add 4-5 drops of Yellow Food Color in one part and mix well with a spoon or fork. I used less since I wanted pastel color. For your perfect color, add 1 drop at a time to reach your color. Now add 7-8 drops of Blue Food Color to the other part of the cake and follow the same instructions as for yellow color. The blue color will give you a kind of lavender tone. For deeper color, use more color.
Now pour yellow batter on one side of the cookie sheet and blue/lavender batter on the other side of the sheet. We want THIN SHEETS of Cake to cut and decorate. Tap the tray and spread the batter evenly.
Bake the cake for about 20-25 minutes till it is fully baked. Start checking for done-ness at about 18 minutes. Mine was done in 25 minutes. This time might vary depending upon the type of oven or the weather outside.
Take the cake out. Let it rest in pan for 10 minutes. Separate the yellow and lavender parts with a knife and then transfer on cooling racks for complete cool down. This will be delicate as it is a thin sheet of cake. Handle with care.
Once the cake is completely cooled down, spread a parchment paper on kitchen counter and transfer the cooled cake sheets to it. Now take a round shape cookie cutter that is 2 inches in diameter. Cut out circles/rounds out of each color cake and set these on cooling racks. Keep the whipped cream ready.