Higher frequency light wavelengths (blue) absorb more in our atmosphere. At sunset, light must travel farther to reach the observer, so more blue light is scattered and the sun/sky appears orange and red.
Since the atmosphere on Mars is so much less dense than Earth's, presumably less light would be scattered and absorbed in Mars' atmosphere. As a result, would the sky at sunset look just like midday? Furthermore, does Mars' sky even look blue from the ground, or is the atmosphere composition different enough that it produces a different color?