Lava tubes can be black as night and totally devoid of any color. Mineral deposits can coat black lava and provide color, usually as white or yellowish crusts. But lava itself can take on many colors in lava tubes, sometimes with spectacular results as seen in the accompanying photos. The color it takes depends on both its chemical composition and oxidation state. Iron compounds will turn red on exposure to air, and red lavas are often found around skylights or other openings that bring fresh air into the tube. Green lava has a high pyroxene or olivine content.