They are not coins, but tokens. "Wert-marke" translates from German as "value token".
Governments are under some obligation to not change the composition of their coinage un-necessarily; it creates confusion and causes difficulties in
Counterfeit Detection, etc. Token-makers are under no such obligation; they are free to make their tokens out of whatever they (or their customers) wish. Indeed, if two nearby shops are both using tokens of the same design, they will probably wish their tokens to have a different appearance, so they cannot be easily interchanged.
The tokens may actually be made of different metals, or one of the tokens may have been plated, either by the token manufacturer or by the end-user of the token.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis