I absolutely cover mine. All of my meads, ciders, wines, beers, etc are in a dark place and covered with a towel or blanket. Cider, mead, and wine don't "skunk" but can get light-struck. It can change the color and flavor of the cider. Dark wines can "bleach" and the flavor can also fade. Light affects tannins, too, so can change the character of wines and ciders. UV light is the worst, but I keep it protected from all light sources.