What do you need to know? Here are the basics -
Light Cyan and Light Magenta do not expand color gamut whatsoever. It is common for sales people to say it does. These colors simply make transitions look smoother especially in skin tones and certain gradients. Most modern printers, including the Mutoh, do not need these colors and the same effect can be done by printing smaller dots of the regular magenta and cyan.
Light Black does add some good functionality to the printer, especially when it comes to black and white printing. Grays have been notoriously hard to print on CMYK printers. Yet again this is a color issue that can be fixed with proper profiling rather than adding another ink to you system and slowing it down.
CMYKx2 is faster than 7 Color by about 50%
Obviously I advocate for the CMYKx2 setup for almost all of my customers. To be fair though, I know for sure that the guys at Correct Color disagree with me and they are the color experts. I totally respect their expertise and if I had a shop I would hire them to make my profiles. However, I would love to see a study to see if anyone can really tell the difference between a 7 color and 4 color print from 3 feet away without color reading equipment.
