Wet vs. Dry
The striking difference in appearance between a wet and dry surface is illustrated well here. A section of beach made of solid bedrock -- in this case the colorful, cobble-infused, Precambrian Copper Harbor conglomerate -- looks much brighter on its dry surface than the wet parts. Light gets reflected between the underside of the water's surface and the rock material, and gets scattered more underwater and within the water-filled pores and rough areas of the rock surface. This all reduces the amount of light that makes it back to the viewer.
1 E Copper Harbor MI (20 Jul 7), looking NW