rationalskepticism.org

GrahamH wrote:

DavidMcC wrote:... The different appearance of the different "yellow" squares..

...is an appearance (i.e. "perceptual colour")

Acually, it's more a matter of shade than hue. The "brown" and "yelllow" squares do not look like very different hues, just very diffeent shades.
I suppose you can define "colour" as including shade as well as hue.