In a microwave-safe small bowl, mix the lemon juice and gelatin and let sit for 5 minutes.
Place the cream cheese in the bowl of a stand mixer fitted with a paddle attachment, and beat over medium speed until it is smooth, creamy, and free of lumps. Beat in the condensed milk a little at a time, occasionally scraping the bottom and sides of the bowl.
Microwave the lemon-gelatine mixture for 10 seconds, or until liquid again.
Add the liquid lemon juice/gelatine mixture and vanilla to the cream cheese mixture. Beat until well incorporated, about 2 minutes.
Divide the cheesecake into three equal portions (each should be about 2 cups). Tint each portion with 1- 2 drops of gel food coloring of your preference, mixing until the color is smooth and uniform.
Spread the first color over the crust; smooth layer with the back of a spoon or an offset spatula. Then, carefully, spread the second color on top of the first and then the third on top of the second; smooth the top. Cover with plastic wrap, and refrigerate until firm, at least 6 hours, ideally overnight.
Before unmolding, run a sharp knife between the cheesecake and the side of the pan. Next, unclasp the sides of the pan, and remove the cheesecake.
Decorate with whipped cream and sprinkles, if desired. Serve.