A set of colorants for printing a multi-colored image when viewed under non-visible radiation outside of the visible spectrum can include a first colorant and a second colorant. The first colorant can be capable of absorbing non-visible radiation and shifting the wavelength of the non-visible radiation to a visible wavelength, thus producing a visible color. Likewise, the second colorant can be capable of absorbing the non-visible radiation and shifting the wavelength to a second visible wavelength, thus producing a different visible color.