Swimming through the oval, saucer-like reflections, dipping and flashing on the sea surface, one traced the colors back to the origins of those reflections. Some came directly from the sky and different colored clouds, some from the golden greens of the vegetation growing on the cliffs, some from the red-orange of the seaweed on the blues and violets of the adjacent rocks, and, all between, the actual hues of the water, according to its various depths and over what it was passing. The entire elusive, unstable, flicking complex subject to the changing qualities of the light itself . . . it was as though one was swimming through a diamond.

-- Bridget Riley The Eye's Mind

Bridget Riley (link)