Something familiar to AppleÖ MacintoshÖ computer users is the color picker which is basically a slice of color space.

1) Hue  is most saturated, or has the greatest chroma, at the outermost edge.

2)  Closer to the center, the hue becomes less saturated.

3) The center axis is controlled by adjusting the brightness value slider.  (Here, brightness is used as a term for lightness, or value.) By decreasing the brightness value, all colors become darker.