I proved this to my own satisfaction and many others a few years ago.

Here's how you prove it to yourself...

Find a picture of the rovers that was taken on Earth.

Find a picture of the same part of the rovers taken on Mars.

There is a color wheel on the rover you can focus on to color correct the picture taken on mars until it matches the picture taken on Earth.

When you are done, the sky will be blue, and the rocks will have many colors other than red. It looks more like Arizona than traditional pics of Mars when you are done.

This can be done easily with Photoshop. Try it.