Important: One thing to note up front here is that not all images actually have any areas in them that are supposed to be neutral gray, and obviously, you can't find what's not there, so if that's the case with your photo, no technique for finding midtone gray will work.
Unfortunately this colour is much more true to blue than green. I now have a soft turquoise but washed the colour out after only 10 minutes. So I'll be surprised if it lasts for more than 2 weeks. Overall I think the Joico colour has great pigment but don't go with the colours you see on the package!!
However, if you read the instructions on most at-home hair coloring kits, youâll find that itâs recommended that you wait at least 24 hours after you color your hair to actually wash it with shampoo. Ideally, however, you should wait as long as possible to wash your hair after coloring.