Cassini took the images used to make these color composites through clear, ultraviolet, green, and infrared filters between March 26 and April 1, 2015. They show Iapetus' north pole above its leading hemisphere, which is coated with dark material that likely originated on Phoebe. The images are enlarged 2x from their original resolution.
To make these images, a color composite was made by combining the ultraviolet, green, and average of two infrared frames into a single color photo. A grayscale image was made by stacking clear, ultravioet, green, and infrared frames in order to smooth out JPEG compression artifacts and reduce noise from cosmic ray hits. The color image was then overlaid on the grayscale image.
Here is an animation of the images.
NASA / JPL / SSI / Emily Lakdawalla
Animation of Cassini's March 2015 Iapetus observations
Cassini observed Iapetus 33 times over the course of a week from March 26 through April 1, 2015.