Pour 1/2 ounce of grenadine into the bottom of each shot glass.
Place the shots in the freezer for 5 minutes.
Use a clean syringe to pull in 1/2 ounce of peach schnapps. Then slowly squirt the peach schnapps over the grenadine so it floats. (see note) Repeat for each shot.
In an extra shot glass, mix together the blue curaçao and vodka. (The vodka increases the ABV and helps this layer float.)
Use a clean syringe to pull in 1/2 ounce of blue curaçao. Then slowly squirt the blue curaçao over the peach schnapps so it floats. Repeat for each shot.
Keep chilled in the fridge until ready to serve, or serve immediately.
Notes
If you don't have a syringe, you can pour the layers over the back of a spoon. Place the tip of the spoon near the edge of the glass and then pour, moving the spoon up as the glass fills.
If your syringe has metric measurements, you need 15mL to equal 1/2 ounce.