Why does the color of cloth turn darker when it comes into contact with water?
The color of cloth depends on what wavelengths of light it reflects; lighter colors reflect more light, darker colors reflect less light. When a piece of cloth comes into contact with water, several things happen. First, the fibers of the cloth begin to soak up the water in accordance with water's surface tension properties and, depending on the fiber, using capillary action. After the cloth is soaked, it usually appears darker to the eye. This is because the wavelengths of light reflected by the cloth surface have changed. Water absorbs and refracts light, causing less of it to be reflected by the cloth and captured by the eyes. By filling in the spaces between the cloth fibers with refractive water, the cloth is able to capture more light than it could while dry, and so the reflected light appears to show a darker color.