Itten was a prominent figure in the Bauhaus movement and developed a theory of color that emphasized the psychological and emotional effects of color. While he didn't explicitly use the phrase "more light a reflects luminous it is said to be," he did emphasize the relationship between lightness and luminosity.

Here's what Itten said about light and color:

* Lightness: He considered lightness a fundamental quality of color, referring to the relative amount of white or black present in a color.

* Luminosity: Itten associated luminosity with the perceived brightness of a color, influenced by its light-reflecting properties.

Therefore, Itten's ideas suggest that the more light a color reflects, the more luminous it appears. While he didn't use the exact phrasing you mentioned, his concepts of lightness and luminosity link directly to the reflection of light and the perception of brightness.