The challenge will be getting the layering right, not just the colours. The heavier stuff goes to the bottom regardless of how you pour it (like Baileys for example) and the lighter stuff will "float" on top. .
True but if you are really careful and use the convex side of a bar spoon, you can layer ones that are slightly different densities. If you don't use a spoon, you need liquors with a greater difference of densities to layer properly.
With a little food coloring, you can get creative. Usually one bottle of dye per twosix of liquor usually works well.
Two shots that work well:
1 Blue Curacao (Blue)
2 Pina Colada Liqueur (off-white but works with dye)
3 Grenadine (red)
1 Midori (green but can look blue with dye)
2 Bailey's (works with Dye)
3 Jager ( lots of dye needed)
Pour in Numerical order!