OK, so we want to cover gray.
2 things to try,
Forget the boxed color and head to Sallys
Use the ash color, the lighter one, with 10 volume
20 comes in those boxes
See how that covers the gray, you could have resistant gray, there is another thing to try, later. try this first.
Then, since demi colors seem to grab very dark on your hair, you will need to shampoo with a color enhancing shampoo
Try Artec, it is not a cleansing shampoo so use shampoo first, then the Artec
You will mix equal parts of Lemon flower, cocoa bean, and white violet
shampoo with that. You can shampoo it over and over again because it accumulates, which is a good thing.
Just shampoo the brassy hair, not the rest.
See how that works, then we can alter the custom blended shampoo formula.