All the red spots you see above are actually areas of Mercury's north polar region that contain water ice. That's not all, NASA's MESSENGER spacecraft, the first probe to orbit Mercury, has also discovered organic materials that are similar to tar or coal. These are purported to have been delivered millions of years ago by comets and asteroids crashing into the planet. Continue reading for a video and more information.
According to scientists, the organic material, which is about twice as dark as most of Mercury's surface, was mixed in with ice delivered to the planet by a comet or asteroid eons ago. On a similar note, the ice vaporized and then re-solidified where it was colder, leaving dark deposits on the surface.
[Sources 1 | 2]