Linda pointed to her ceiling. “What color is that?” she asked.  Not realizing this was a trick question, I immediately replied, “Slate blue.” Of course I shouldn’t hesitate.  We had just met only minutes ago.  What kind of decorator hesitates to answer such a simple question?

Turns out, a GOOD one.  Linda’s ceiling is, in fact, green.  She proved it to me by taking me into another room and showing me the same paint on her dining room wall. 

Her home already had green wall to wall plush carpeting and a sage ceiling when she moved in six years ago.  She began to decorate it with her own touches, so she painted the walls of the Family Room a deep gold to try to bring her palette into the space.  But something happened.  Before her very eyes the ceiling morphed to blue.

I know this phenomenon exists.  Even though I self-identify as an artist, I am infatuated with science.  I know the “science” of color.  This is the first time, however,  I had seen such a dramatic example.  The ceiling is partially shadowed, and is viewed from below.  Our brains, not our eyes, transform the color. From Discover:

“Neuroscientists have long believed that evolution hardwired the brain to amplify slight differences in shading, making it easier to perceive subtle details like a green snake in a green tree. Thus objects on dark backgrounds appear lighter than they are, and those on bright backgrounds appear darker. But science advances by replacing approximate truths with more precise ones, and new research suggests that this scientific “truth” is, at best, incomplete. The two experiments that follow help show why the thinking on this subject is changing…

…What are the colors of the squares indicated by the arrows in the two figures at right? For most observers, the one on the top looks blue and the one on the bottom looks yellow. But the two squares are actually an identical shade of gray. One possible explanation for this illusion is simultaneous contrast, a process by which your brain makes foreground objects take on the opposite hue of their backgrounds in order to improve your discrimination of subtle color differences. According to this theory, the top square appears blue because the figure is on a mostly yellowish background, while the bottom square looks yellow because it’s set against a predominately bluish background.”

More here.