Why did Bridget riley mostly paint in black and white?

Bridget Riley predominantly used black and white in her artwork to explore the effects of optical perception and to emphasize the formal qualities of her compositions. The stark contrast between the two colors allowed her to manipulate shapes and patterns, creating dynamic visual experiences that challenge the viewer's perception. By focusing on these extremes, Riley was able to highlight the interplay of light, shadow, and movement in her work, which became central to her artistic exploration.