Astronomy Picture of the Day . Dark Spots on Neptune . ... Credit: Voyager 2 Team , NASA Explanation: Neptune has spots. The Solar System 's outermost gas giant shows a nearly uniform blue hue created by small amounts of methane drifting in a thick atmosphere of nearly colorless hydrogen and helium . Dark spots do appear, however, that are anti-cyclones : large high-pressure systems that swirl in Neptune's cold cloud tops . ... Publications with keywords: neptune - Solar System . ...