This image shows the multiple layers of a hot-stamp foil (ribbon).

The bottom "adhesive layer" is what is pressed against the chip. At the top of the drawing, the "PET Carrier" gives the foil roll the strength to run through the machine. The "Release" layer (typically wax) allows the next 2 layers to separate from the Carrier and remain on the chip. Note that the "Colored Varnish" layer is the coloring we see in the hot-stamp, red, blue, gold, silver, etc. And then there is that "Aluminum" layer, which gives a consistent strip of material to hold the "Colored Varnish" layer and the adhesive.

If and when the "Colored Varnish" layer gets worn, or does not hold well to the "Aluminum" layer, the Aluminum layer will show through.

And what color is natural aluminum?... silver!