Ignore the “Orange Drop” nonsense.
Ceramic, Mylar, Polypropylene, metallized polyester will all work the same.
I like Orange Drops just because their size and shape makes them easier to handle, and their color makes it a little easier to see what's going on inside a crowded control cavity. Aside from that though, as far as guitars go, the cap type doesn't mean a damned thing.
I agree with the above. Ceramics, greenies, whatever. Furthermore, I don't worry about a tone cap being a little out of spec. In practice, it amounts to a tiny nudge, one way or the other, of the knob.
Also, you can come up with odd values by combining caps in parallel. An example would be putting a .022uf cap across the legs of a .047uf cap to get very close to .068uf
Do you know of a website or some resource that lays out these basic electronic principles (like .022uf in parallel with .047uf in parallel = ~.069 uf, what the difference would be if in series, etc.)?