The image, aside from being visually stunning, highlights one of the more alien aspects about Mars.
You see unlike the day/night cycle here on Earth, Martian sunrises and sunsets are a glorious blue, while the days themselves are a deep rust-coloured orange/red.
So what causes this stunning phenomenon? Well fine dust particles in the Martian atmosphere absorb most of the blue light, causing the daytime to feature the deep orange colour we see in photos and in films.
However during sunrise and sunset the particles directly facing the sun reflect the blue light back giving it this beautiful light blue halo effect.
Curiosity sadly doesn't take these images very often, however when they do the results are always pretty spectacular.