Today in part I of our daytime series "Dark Shadows," we ask the question: "On the walls, looking like blue-green velvet, was it mold or something far more sinister?" Dark shadows show up around the house in different places for different reasons. Mold, caused by high indoor humidity, could be the culprit. Many surfaces support the growth of mold. Moist bathroom tiles, grout lines and damp walls and ceilings are common breeding grounds. Mold can be an aesthetic problem or, for some, a serious health issue. Either way it's not a pretty picture. To clear it up, start by getting humidity under control. Then tackle surface mold with a mild solution of household bleach in warm water. If that doesn't work, it probably isn't mold, And that brings us to tomorrow's episode of "Dark Shadows" where in part II, we ask: "So is it dirt or what?" Stay tuned. And that's the On The House tip for today.