What is a color scale
It is the series of shades that come from one color: from an almost white version to an almost black one. They all share the same base hue, so they always go together.
Tints, shades and tones
A tint is the color mixed with white: lighter and softer. A shade is the color mixed with black: darker and deeper. A tone is the color mixed with gray: more muted and elegant.
How to use a scale in your design
Use the light steps (50 to 200) for backgrounds, the middle ones (400 to 600) for buttons and links, and the dark ones (700 to 950) for text and borders. One scale gives you a clean, consistent interface.