They are spectacular in blue light. These ground fogs and frost deposits make can deceive one into believing the Polar Cap is much larger and apparent than it really is. These areas also can show in the reds to a lesser degree. The Reds and to a lesser degree the Yellows penetrate through the atmosphere of Mars to enhance the definition of surface details. Desert areas appear bright.
Dust storms can appear bright as well.
The image of Mars alternating between red light and blue light demonstrates how blue emphasizes the atmospheric features while the red light enhances the surface features. Although the origin of the UV features remains a mystery to this day, it is generally believed that gaseous sulfur dioxide and chlorine, the latter produced by the photo-dissociation of hydrochloric acid in the upper cloud layers, are responsible. Both of these substances strongly absorb short-wavelength radiation.