Is it possible to make transparent / translucent pastry?

With great skill, a true artist could do what you describe with Thai/Vietnamese rice paper, the dinner plate sized, extra thin ones, like for Fresh Spring Rolls.

I will never apply for the job, I promise.

I respect Jolenealaska's creative thought, but nothing truly resembling pastry is going to be translucent or transparent unless it is exceedingly thin. The structure alone will refract light, making the product opaque in the same way snow is opaque even though individual water crystals are fairly transparent, if they don't have air inclusions.

This is because any real pastry will have a complex structure of starch, fat, protein, and so on.

While I respect the idea of trying to use a very thin noodle (which is only really somewhat translucent because it is thin, much like tissue paper), that is not likely to be delicious, and will be somewhat incongruous in a western style savory pie.

Instead, I suggest you achieve your goal (making it clear which pie is which) by the more traditional means of one or more of:

• Different crimping styles at the rim
• Using different patterns for the steam vents
• Cutting out and baking on crust garnishes in different shapes for different types of filling; you could even cut out letters

Less traditionally, at least for savory pies:

• Use a lattice crust, so the filling is visible, but you still have some pastry on top
• Use food coloring, or natural ingredients like beet juice or annatto to color the pastry, with different colors for each pie variation

For example, one Caribbean restaurant near me has vegetable patties (a hand pie) with pale crust, and chicken patties with a pale greeny-yellow crust (not sure what they use, probably a touch of their curry mixture), and beef patties with a richer orangish colored crust (they might have used annatto).

If you want the least obtrusive flavor, the best you can go with is thickened water.

While you can probably prepare sheets with the right hydrocolloid and lots of care and plastic foil, I would suggest choosing a thickener which thickens on cooling, and pouring the warm mixture over the pie. Arrowroot starch is frequently used in this role on fruit pies, I don't see a reason why it shouldn't work on savory pies. But if you have meat in the pie, a gelatine texture would probably feel more natural. In both cases, don't add anything to the mixture, just the thickener and water, and process in the usual way.

While it wouldn't be a pastry, per se (or at all), using discs of cast sugar might work for what you need. If you poured thin disks of cast sugar into a ring mold the size of the top of your pie, you could probably attach them with marzipan or a starch wash or something after cooking the pie. If they were thin enough, you should be able to cut through them to serve the pie (though they probably wouldn't cut neatly).

I agree with the previous answers on several other points though. You could use something akin to a Korean sweet potato noodle. They are exceptionally clear, but the gummy and chewy texture probably wouldn't do a pie any favors. Anything resembling a more traditional pastry is going to be opaque (even a single layer of phyllo dough is opaque when baked).