Arrange 30 2-ounce plastic cups on a baking sheet. Set that aside.
In a medium mixing bowl or spouted measuring cup, whisk together 1 cup boiling water and the 3 ounces red jello until completely dissolved. Whisk in 1/2 cup cold water and 1/2 cup vodka until combined.
Pour the red jello into each of the plastic cups, filling them 1/3 full each. Place the baking sheet with the cups in the fridge for 1 hour.
After 30 minutes, whisk together 0.5 ounces unflavored gelatin and 1 cup boiling water in a medium mixing bowl or spouted measuring cup until completely dissolved. Whisk in 14 ounces sweetened condensed milk and 1/4 cup vodka until combined. Let cool for 15-30 minutes. (see note)
Take the shots out of the fridge and pour the white layer over the red layer, until each cup is 2/3 full. Chill the shots for 1 hour in the fridge.
After 30 minutes, whisk together 1 cup boiling water and 3 ounces blue jello in a medium mixing bowl or spouted measuring cup until completely dissolved. Whisk in 1/2 cup cold water and 1/2 cup vodka until combined. Let cool for 15-30 minutes.
Take the shots out of the fridge and pour the blue layer over the white layer until each cup is full. Chill the shots for 2 hours in the fridge, or until completely set.
Just before serving, top with Whipped cream and Red, white & blue sprinkles if desired. (see note)
Notes
1 packet (0.25 oz | 7g) of Knox unflavored gelatin is equal to 2 ½ teaspoons. If you buy a canister or pouch of gelatin instead of packets, you can just pull out your measuring spoon.
It's important to let the jello cool down some before pouring it over the previous layer. This will help ensure it doesn't melt the underlying layer and blend the colors together. It's equally important to chill each layer for at least 1 hour before pouring on the next layer, for the same reason.
Gelatin causes whipped cream to break down (quicker than you might expect). So it's important not to add it on top until just before serving these shots. You can use Cool Whip if you prefer, as it will last longer.