Think of him as a piano virtuoso redesigning his instrument so that each key looks like the note it struck.
Excerpts of The Sounds he Sees from Stanley Whitney: Dance the Orange - The Studio Museum in Harlem Exhibition Catalogue (43) , by Robert Storr (2015)

Roberts Storr couldn't have put it better. Synesthesia may seem to be the first word that comes to mind, when we think of Stanley Whitney's rhythmic color field paintings, with which he has been experimenting since the 1970's.
Stanley Whitney (Philadelphia, 1946) is a New York based painter who grew up in a musical filled environment in Philadelphia, a heritage he often mentions in interviews as his initiation to artistic life. His frequent trips to Italy have also been very influent in his work. He holds a BFA from Kansas City Art Institute and an MFA from Yale University, where he studied when Josef Albers was the program director, and often visited Robert Rauschenberg's studio. Whitney is currently Professor emeritus of painting and drawing at Tyler School of Art, Temple University. His work has been shown in galleries and museums such as the Contemporary Art Museum of Houston, TX, USA (2014); Cheim & Read, New York, NY, USA (2013); and at the 50th Venice Biennale (2003); he is also present in numerous public and private collections around the world, and has been awarded a Guggenheim Fellowship (1996).

I got to that format because I want to get to the color immediately. I don't want to have to work on a drawing, work on a structure, and then add the color. So this format allows me just to get to color. (...) With this kind of system, it allows me a lot of freedom. The paintings are all the same, but they're all totally different. I think about them almost like people - we're all the same, but we're totally different.
(...)
The painting tells me when it's finished. When everything in the painting equals out, and no color gets in the way of any other color, and they have good transitions, then I know it's finished. (...) When things are really democratic and equal, I know I'm finished.

Stanley Whitney interviewed by Hans Ulrich-Obrist at his NY studio (2019)
 

More on Stanley Whitney, here.