How to tell film capacitor type
There is NO solid answer to your question.


The capacitors shown look to be Mylar (reddish-brown), but I have also seen them with dark green coatings. I have some large reddish-brown 1uF 630vdc capacitors with the same body shape, but they are made with a polystyrene dielectric.
Depending on shape and size and manufactures specs, the wrapping or coating may change to accommodate assembly procedures and how the capacitor is sealed against moisture. I am used to ceramic disc capacitors having a light brown color, but that is not a standard set in stone. Ceramics can be small block-style and colored yellow, or dark brown for smd versions.
I have used large 3KVDC .15uF polypropylene capacitors made by GE that were wrapped in yellow, but without the datasheet and the fact that I ordered them as a pulse filter, I would have no way to know the materials used. At least these had part numbers on them, but most capacitors on a PCB do not have room for more than a capacitive code and voltage-if that.
The bottom line is that if the coating is not obvious from constant usage of that type of capacitor, and there is no part number, your out of luck. No practical way to find out unless you cut one open and use chemicals to test what the dielectric is made of.


EDIT: As shown by Robert Endl's testing for dissipation factor with different dielectrics, if one has the need to, a DIY chart can be created that shows how the dissipation factor changes for a given dielectric type, all having the same capacitive and voltage value. This would be helpful for capacitors out of a junk bin that can be sorted with a good LCR meter.

Of course the chart must be created first with known dielectrics before sorting unknown dielectrics can be done.