This is an example of a grayscale print that can be achieved with an unmodified Ultimaker 3. This was designed and textured by Beerend Groot.
Greyscale printing is achieved using a technique known as linear halftoning. With most 3D prints, you are limited to monochrome, but this allows you to print items in two colors, giving an item enhanced depth, definition, and realism when compared to a monochrome print.
I have written an article about it here.
The feature is not implemented properly in to Cura at this time, but there are instructions of how to test it (for experienced users!) instructions for this and a discussion on the forum can be found here.