Clouds and Sand on the Horizon of Mars . ... Unlike other Martian vistas, few rocks are visible in this exaggerated color image mosaic . The distant red horizon is so flat and featureless that it appears similar to the horizon toward a calm blue ocean on Earth. ... The red dust in the Martian air can change the sky color above Mars from the blue that occurs above Earth toward the red, with the exact color depending on the density and particle size of the floating dust particles. ...