
In the acrylic painting Zing 1 (1971), she introduced the theme of the colour twist, where twisted vertical stripes create horizontal bands. The works from this period are emotional yet peaceful. The response to colour became a more central focus of Riley's works in the 1970s. As exemplified in the canvas Cataract 3 (1967) she began using consistent, stable forms such as the wavy line, and relying on the visual effect of groups of coloured lines (usually faint) in the spaces between to create the desired sensation of movement. It was a cautious foray at first, as a common perception of colour is that it does not disrupt stable elements in as crisp and orderly a manner as black and white. Having set form free from its descriptive role through her black and white works, in 1967 Riley turned to colour. Her work Current (1964), made of synthetic polymer paint on exhibition board, fronted the exhibition catalogue. Riley represented Op art to the world alongside artists such as Yaacov Agam, Richard Anuszkiewicz, Frank Stella and Op art's earliest proponent, Victor Vasarely. The 1965 Museum of Modern Art exhibition, The Responsive Eye, drew international attention to the work of Riley and other Op artists. Riley abandoned teaching and advertising in the mid-1960s as her art practice expanded. Her first solo show was in 1962 at Victor Musgrave's, Gallery One. In 1961, due to increased scale and a need to retain precision, she began working with assistants to produce her work. These combinations form impossible shapes that appear to move, pulsate and undulate before the viewer's eyes, producing sensations of falling and wave-like motion. In the 1960s, Riley began to develop her trademark style: abstract geometric patterns in black and white, composed of curved parallel lines and dots, checkers or triangles arranged in disorienting grid-like or spiral patterns.

In 1960 she also entered the employ of the J.

During the late 1950s and early 1960s Riley took up several teaching positions in the U.K, including the Loughborough University School of the Arts, Hornsey College of Art and Croydon School of Art. Her earliest works were semi-Impressionist figure paintings, followed, from around 1958, by pointillist landscapes. Riley studied at Goldsmiths in London, between 19, and continued her education at the Royal College of Art in London, from 1952 to 1955.
