YuleB...I see nobody has responded to this post...I can tell you what I do...I go the Walmart and find a color that is very close to my hair color or unit....and usually go 1 shade lighter.,...when I apply I usually leave it on for about 10 minutes...rinse it out a make a color check....if it is not dark enough then I reapply...this is not the best technique in the world to darken a unit...BUT it works for me. Cheers