Saturation refers to the perceived vividness of a colour.
- When colours are more saturated, our eyes interpret it as a colour’s luminance and chroma. This makes us believe that the colours are actually brighter.
- As saturation decreases, colours appear dull and washed out until all colour disappears leaving only a grey tone.
- On many colour wheels, saturation increases from the centre to the edge.
https://en.wikipedia.org/wiki/Colorfulness#Saturation