When Does Purple Become Brown and The Case of a Mixed-Up Jacket

Two colorful things happened on one recent week: I painted my nails deep purple for a party and bought new dark brown carpets for our bathroom.
My husband, on his return from a business trip, puzzled me when he remarked that the “purple” carpets seem too dark. “They were very brown when I bought them,” I said and rushed to double-check. After spending two frustrating months on choosing our home wall colors, I knew very well his strong dislike of anything purplish. Surprisingly, the carpets did look dark: purple or brown, one could not say. My deep purple nails appeared to be identical to the carpets.



So, I went on a quest, trying to figure out how two very different colors, brown and purple, can appear exactly the same. And when does purple become brown?

Playing with an online Color Tool, that decomposes any color into Red, Green and Blue components, I realized that both, brown and purple, have very little green in them, and much more red and blue. By taking brown and adding some blue to it we get purple.


So, the answer to the mystery should be in blue. Aha! Perhaps we cannot distinguish between brown and purple in some lighting? Turns out, this is true! “White lights” such as strong skylights and white fluorescent lights as in shopping centers have a lot of blue in them. See the hill on the left graph above the blue. “Yellow lights” such as sunlight and the incandescent light of my bathroom have much more yellow and red than blue in them – see the curve on the right picture.

Light is energy. Here is how it is distributed for “White” Skylight and “Yellow” direct Sunlight.

The color of the object that we perceive is a combination of its color and surrounding illumination (light coming from the light source such as lamp, sun or reflected from other objects).

A simplified color equation:

Object color that we perceive = Object’s “true” emitted color X Illumination

Therefore, any blue in the object is amplified by a skylight or fluorescent light, making it appear even stronger blue to our eyes. The yellow light of the incandescent bulb or direct sunlight on the other hand, highlights the warmer tones, suppressing the blues. That explains why my brown carpet and my purple nails appear exactly the same in the yellow-ish bathroom light and look very different in the fluorescent light of the store.

What is the use of it all, you may say. It tells us that instead of exclusively considering the color of our purchases at the store, we should consider the color as it appears in the lighting conditions this purchase is intended to impress. Buy, try, and perhaps return. Otherwise, your Holiday purple dress may look too brownish for your taste, and those shiny light purple eye shadows may not be a good match at all.

If you are carefully choosing a fancy blue shade of color for your room – make sure you have plenty of white light in it, otherwise your visitors will just call it plain blue.

Great example from the Benjamin Moore page: the same Greyhound color appears drastically different under various light situations.

And if your kid comes home with the wrong color jacket, don’t worry about color blindness and don’t argue – everything will look different in the morning light.