If you go with the presumption that NASA is faking everything, then it's pretty easy to make claims such as this. If there is any evidence to the
contrary, then you can just say that it's fake and leave it at that.
That being said, there is a kernel of truth in the blue sky thing. When Viking photographs were released, they showed a blue sky, but were later
deemed incorrect and were later tweaked, making the sky pink as a consequence. This wasn't because they decided that the sky "should be" pink and
had that happen; it was done by taking a harder look at the way the Viking camera captures pictures. Color calibration on Mars is a very, very tricky
thing, especially when the camera doesn't capture the same wavelengths of light that a normal camera on Earth would use. Planetary scientists are
much less interested in having grand vistas with accurate colors than in getting detailed images with good contrast, etc.
Anyways, the general consensus is that the Martian sky is a pinkish color because of all the fine dust suspended in it. If not for the dust, it would
be a pale blue. This isn't because of a thick nitrogen/oxygen atmosphere identical to Earth's or anything; it's because of
en.wikipedia.org..." target="_blank" class="postlink">Rayleigh scattering, which happens with many different gases, including carbon
dioxide.
The fact is that scientists don't look at colors to determine atmospheric composition. Landers have had pressure sensors, mass spectrometers, etc,
and orbiters/fly-by craft have had sensors too. I'm pretty sure that the thin Martian atmosphere was discovered in 1965 with Mariner 4's flyby.
Every single other orbiter and lander from the US and Europe has agreed with the fact that the surface pressure is around 6-7 mbar on average. In
fact, landers have been
built around this fact. Atmospheric entry is a very tricky process, and very tricky on Mars due to the thin atmosphere.
If it was as thick as Earth's, then the airbags/thrusters as seen on all past, present and future landers would be completely unnecessary.
Of course, you could dismiss all this evidence as some massive joint NASA/ESA cover-up, but ask yourself this: which is more likely?