Several different high-speed digital color-printing technologies have emerged recently after more than a decade of development worldwide. The Xerox Docucolor iGen3 Production press utilizes a unique Image-on-Image color electrophotographic architecture that is advantageous for productivity, image quality, substrate latitude, and run cost. The team developing this product and the Image-on-Image marking technology faced many design challenges on the way to market. This talk reviews the history of digital color printing technologies, the Xerox Image-on-Image marking process, the key technical challenges, how they were overcome, the performance achieved, and the potential of this technology.