You are welcome.

I would think that messing with the colors doesn't mean the pictures are totally fake.

Of course. But it does mean that NASA lies.

Since Mars is known as "the red planet," adding red to the images could "sell" the photos to the public

It is possible. But it is still a lie.

It could be political thing to cut any dreams of abandoning Earth authorities. What will you think when you saw blue sky and usual landscape on another planet? "Wow, it looks fine, it is not scare, may be I even could live there, or at least it will be interesting to see it by my own eyes". But if you see something alien and deep red, it cut the desire to reach that place.

For many years they thorougly make space look scare with all that vacuum, radiation, difficulty, etc, but really it is not.

The pressure difference is only 1 atmosphere, even usual commercial plane body could withstand it without any problems for passengers, it is only 0.25 atmosphere on the 30000 feet altitude where passenger planes fly.

Radiation is not a big problem too - Curiosity had a sensor on board and recorded radiation levels on its way to Mars being in its capsule. So it is recorded what will human experience in a regular nowdays spaceship on the way to another planet. It is interesting, that equivalent of radiation dose in the 6 month flight to Mars, is the same as 1 year on ISS (world record of LEO habitancy is 878 days by Gennady Padalka, and guy is absolutely healthy, still ready to fly and interesting person, who once told in interview for MSM that there exist a secret precept of behaviour in case of meeting with aliens, later he told that it was a joke, but who knows...) or 2 years of work on nuclear station and definitely far below really dangerous for humans level. And if you take a minimum measures for shielding a spaceship, slightly more than thin aluminium sheet, radiation in interplanetary flight will be on the level of ordinary plane flight.

I think there is some special, not very noticeable, but constant fearmongering propaganda about the space travels.

Returning to NASA, when they was caught with colors, they began to think out some senseless bullshit, like "it was done for geologists to allow them better determine geological things". Really, true color of rock is very important property of rock for any geologist.