In our study of color, we see a great many color schemes. What is optical color (not Op art!)?

In our study of color, we see a great many color schemes. What is optical color (not Op art!)?
In our study of color, we see a great many color schemes. What is optical color (not Op art!)?
In our study of color, we see a great many color schemes. What is optical color (not Op art!)?