What does 'freedom of color from white or gray' mean?

Question

The dictionary entry for the word chroma says, "the purity of a color, or its freedom from white or gray."

What does that statement mean? What is color made of? What causes color?

I was reading this link and my interpretation, in the most lay terms, is that color is caused because and when the light that reaches our eye is different from the light that was discharged from a light-source.

This could happen due to:

1) Some of the light being absorbed on its way to our eye; or 2) Only a selected/filtered band of frequency/wave-length of light rays reaching our eye out of the whole spectrum that was discharged from the light-source; 3) Other reasons, which are more or less variations of the single most important fact that color is created because of a variation in the amount or intensity of light that reaches our eye.

Is my understanding correct?

What then is the meaning of the phrase, "the purity of a color, or its freedom from white or gray?"

Answer 1

In the world of paints a freedom from white or grey means just what it says; a colour that has not been cut with white or grey. I have been mixing colours in a paint shop, a long time ago.

Often we would cut a colour to have it more pleasing to your eye. For example a pure blue house paint looks much better when slightly cut with grey or white. Often seen example is pure white though. You don't want blinding bright white paint, really. When I was mixing colours into base paints we used two drops of black ink and one drop of yellow ink into a litre of pure white. The result is still observed as white, but much more pleasant than the pure white.

To have a chroma colour in paint we would mix only pure color ink(s) into clear base paint. No cutting with white or grey.

Answer 2

Wikipedia has a good explanation on this topic. Basically, in color theory, colorfulness is the degree of difference between a color and gray and chroma is the degree of colorfulness relative to brightness from one color to another color that is perceived to be white in the same viewing conditions.

So, if white/gray/black have all wave lengths (or none) in equal measure, so they're achromatic. A color becomes more chromatic once a particular hue becomes dominant. If it's only that hue present then it would be free from white or gray.