The U.S. treasury, and just about everyone else, buys a special kind of black printing ink from a Swiss company that promises not to sell your tone to anyone else. The ink has special ultraviolet properties that are difficult to imitate. North Korea buys the same ink from them in Magenta. The North Korean “supers” use the altered magenta formulation.
Unless your currency is backed by gold or silver, it’s all counterfeit. Every greenback in circulation today is counterfeit. For further information, read Murray Rothbard.