Currently its very difficult getting precise colours using the picker. sliding the hue shifter on the right is just too sensitive due to the small size and vast range of colours it covers.
Separate sliders for R,G,B would be good, it would give use 3x more accuracy compared to the 1x hue slider.
To clarify, I know you can manually enter a colour value, but that involves you having to know the colour you want and its value. for people who want to just browse colours and fine tune them, it's very difficult at the moment.