What is the difference between hi-lites and lo-lites? When is it recommended to have one or the other?

The most natural look for grey hair is to cover the whole head with hair color and then go back and put in lighter shades --highlights.  An expert hair colorist knows how to do this so that you will have a natural look and not cause damage to your hair.  Your color will look good as your hair grows out.  Sometimes darker shades, lo-lites are strategically placed-- for special effects, to enhance the lines of the cut.