[Tuna-Fish]

There are color laser printers.

On a monochrome printer, I guess you can still to steganography by messing with the dithering, I guess? However, since the stated aim of the fingerprinting is to catch money counterfeiters, I guess they are less interested in monochrome.

[minikites]

Are any major banknotes monochrome?

[snypher]

Each layer is, but that's probably more advanced than just "printing a banknote".