Color Theory defines a True Tone as any Hue or mixture of pure colors with only Gray added. To be precise, this definition considers Gray as truly neutral. In other words, there are no additional pigments in the Gray other than White plus Black.
A neutral mixture of Gray, no matter how light or dark, will tone down the intensity of any color. As a general warning, be careful with how much Gray you mix in. Too much Gray dulls the color so much, it becomes impossible to get the brilliance back.
Toned colors are generally considered more pleasing to the eye. They are complex, subtle and sophisticated. That's because bright pure colors are most often associated with children.
Credit: Color Wheel Artist