just a little tip, to take the sting or burning sensation away during color just add some sweet-n-low to the color it's self or directly on to the scalp after applying color. it really helps cool the scalp . i know from personal experience.
I have been using sweet-n-low in my bleach for about 20yrs now and its never failed me yet. You see its the saccrin in it that neutralizes the chemical reation to the scalp/fingers/skin in general.
I remember hearing something about this. I know that sugar helps when you burn your tongue! I will have to try this with the sweet and low, I have had a few clients who are sensitive to color or bleach.