Chromoplast, in German where they are made is their product- trade name.

they are a laminate .. a metal foil
(it can be a wiring path to a taillight, because there are stripes that are actually separating the foil strips)

in between layers of a Thermoplastic that is the structure , of the mudguard .

I have several sets on various bikes , the black is the color of the plastic*
as is the silver-transparent, plastic, showing the foil .

*meeting your definition.