Color & LightRevised
Saturation
The purity or intensity of a hue, independent of how light or dark it is.
In practice
Saturation describes how vivid a hue is, from a pure, intense version to a grayed-out one, while its lightness stays a separate matter. Designers adjust it to control mood and focus. A banking app might use low-saturation blues for calm background areas and a single highly saturated orange for the one button that must be noticed. Many fully saturated colors side by side tend to vibrate and tire the eye.
Often confused with Tone
Saturation is how pure or grayed a hue is; tone is how light or dark it is, so a color can be dark yet fully saturated.
Try this
Lower the saturation of one photo in steps down to zero and note the step where the mood changes most.