Chiaroscuro refers to the use of strong contrasts between light and dark to create a three-dimensional effect. It was pioneered by the painter Caravaggio and involves illuminating dark scenes with shafts of light. The level of light or darkness used in an image, whether it favors shadows or highlights, can dictate the mood conveyed as either low key or high key. Color plays an important role in composition, with hue, saturation, and brightness determining each color, and relationships between different colors like complements and harmonies evoking emotional responses.