Jim Hamilton, Group Director at InfoTrends has a blog post up at InfoTrends’ InfoBlog comparing digital printing systems that have the capability to use more than 4-colors in print applications. Jim says,
I’ve been giving some thought to devices that offer one or more imaging stations above the typical four (for the four process colors). HP Indigo, Kodak NexPress, and Xeikon have had this capability for many years but recent announcements are expanding this capability, and, in addition, others are entering this space. The possibilities range from simple spot color use to custom colors, coatings, and magnetic image character recognition (MICR).
Take a look at the table at Beyond Process Color Digital Printing: Approaches to Additional Colors, Special Effects, and MICR