We can finally be sure that the Martian sky is blue. Updated 2/10/2016.
This page will update the controversy about Mars sky color that has raged ever since Viking 1 landed on Mars. You can see how the color issue was handled then on my Mars Sky Color Page. This article will advance the issue to what is being seen on the newly landed Mars Science Laboratory Rover Curiosity.
Figures 1 (above) and 2 (below), unlike the first color photo back from the Curiosity on Mars (Figure 3) that was taken with the dust cap still over the camera, show a pale blue sky in images that look like Earth.
Figure 3 – The first color photo received of the north wall and rim of Gale Crater where NASA’s MSL rover Curiosity landed. The picture was taken by the rover’s camera at the end of its stowed robotic arm and appears fuzzy because of dust on the camera’s cover. This dust is what I think has clogged all pressure sensor dust filters sent to Mars so far, including the FMI Vaisala dust filter that flew on Mars Phoenix. That system is identical to the one carried on MSL.
Figures 4 and 5 - Note how similar the color of the sky shown above on Figure 3 (taken from CURIOSITY) appears to the color on Figure 4 taken from OPPORTUNITY. Figure 5 is supposed to be false color.
Figure 6 below shows the rel and falswe colors from Viking 1 and greenish spheres, likely alive, seen from MSL.
Figure 7 below: On August 27, 2012 the sky color is still holding at a pale blue. This looks like Earth. It is not clear if colors are enhanced or altered.