Color is the vibrance in our world , we see it everywhere and color has many effects from our eyes to our brain. This subject is deep and you should look into Color Physics.
Color and the Wheel
The Color wheel is mainly separated into primary, secondary and tertiary colors. Read about color schemes to better understand these systems.
Color and ValueWhen you want to tint a hue you add white, to tone it you can add gray, so naturaly you would add black to shade it.