Hi, F!
In color photography, the negative's colors differ from the positive's; e.g., an area that is green in the negative will become red in the final print; and conversely, a red area will be output as green.
So too in Faldage, as I understand it, a yellow input (beer) is transmuted into a clear output; and conversely, a clear input yields a yellow output.

Now faldage, please don't be put out by my input!