Wella Colour Touch 1.9% or 4%?

[morgan2705]

so I have brown hair already but its faded and I just want to re-colour it so I have the Wella Colour touch shade 4/0 and it says to use either 1.9 or 4 percent Emulsion but I don't know which one I should use any suggestions?? what is the difference?

 

[AcidPerm]

What level is your natural? Are you doing a root retouch or changing the colour?