Earth and Sky【1】

Sometimes you hear it said that white is a combination of all the colors of the rainbow —— and that black is the absence of color. Find out more about whether black and white are colors —— today on Earth and Sky.

　　JB: This is Earth and Sky. A listener wants to know,"Are black and white really colors?"

　　DB: Color isn't a physical quality. It's a phenomenon of light and perception. Matter and energy are colorless. It's really our eyes and brains that make a fire-engine red or chickens white.

　　JB: Colors are defined by their hue, saturation, and value. Hue is what we think of as making blue blue, and not orange or grey. Saturation refers to a color's vividness —— it's what makes a pale blue sky different from one that's deep blue —— or pink different from red. Value refers to a colored object's lightness, darkness, and brightness —— that's the contrast between, say, the shining moon and a glass of red wine.

　　DB: It gets pretty complicated to talk about what makes a color a color —— because colors can only be talked about in terms of themselves —— and how they differ from one another. Black is black precisely because it has no redness or greenness or any other hue. But, to answer your question, black and white —— and grey, for that matter, too —— are colors. They're neutral colors —— different from each other only in terms of their darkness and lightness. Like all colors, black and white are products of our visual processes —— they exist only because we're there to sense them.

　　JB: To ask us your question, come to earthsky.org. With thanks to the National Science Foundation, we're Block and Byrd for Earth and Sky.