Which is the brightest, an overcast sky, snow covering the ground or a white wall?

that cold-hearted orb that rules the night removes the colors from our sight red is gray and yellow, white who decides which is right, and which is an illusion

The person who wrote this either spent too much time staring out the window and daydreaming or was a keen observer of the nature of light and color. Brightness is the only quality in which white, gray and black are different, and the surrounding background is what we use to determine how bright an object appears. Have you ever noticed that when you look up at snow falling from the sky, that the snowflakes look darker than the sky? But when the sky is overcast and gray, it looks much darker than the snow covered ground. Why is this so? It is the sky which illuminates the surface and makes it appear dull or bright. An object illuminated by the sky cannot be brighter than the sky itself. The contrast between the snow and the much darker shrubs, trees, pavement, or buildings gives the illusion that snow is brighter than the gray sky. The same is true if you look at a white wall on a cloudy day. You may be able to confirm this by placing a mirror so that the image of the gray sky is seen next to the snow or to a white wall. The snow and the wall should look somewhat darker than the sky.

The above verse is from the song "Nights In White Satin" by the Moody Blues (or is it the Moody Grays?)

You are sitting in your classroom looking out the window daydreaming (in reality this probably never happens). The sky is overcast and clouds obscure the Sun, it snowed several inches the other day and across the way you see a wall which was recently painted white. Which of these three things (the sky, the snow or the wall) is the brightest?

01/26/96