In order to choose color mode that fits your needs you have to know for which technology you're preparing graphics. The aim of this tutorial is to lead you to right decision.
Even the best industry-standard printers have great difficulty printing more than 50 distinct shades of grey (i.e. 'Monotone'). To enhance this greatly and improve underlying tonal quality, a second color is often added, making the image two-color (or 'Duotone').
