HSV color picker using Unity UI
Unity 2018
Unity 2017
Unity 5.6
2018 is default, unity 5 and 2017 can import the assets just fine.

public Renderer renderer;
public ColorPicker picker;
// Use this for initialization
void Start ()
{
picker.onValueChanged.AddListener(color =>
{
renderer.material.color = color;
});
renderer.material.color = picker.CurrentColor;
}
// Update is called once per frame
void Update () {
}if you want to assign your own color first, just do this call and it sets the slider and picker to the proper selection.
Color color = Color.green;
picker.CurrentColor = color;