Topic: Cassia for ash blonde?

Hi, i am new to this, my natural hair colour is medium ash blonde, i am trying to get rid of and tone down brassiness from colour that was supposed to be ash but it seems everything turns some shade of yellow on me which does not suit my cool toned complexion. i am trimming this old dye out as i grow but is it possible to make a mixture using the cassia and amla only to cover a small amount of grey but still keep the ash colour? if it can't cover over the other dye that is fine but for the new virgin hair coming through is there a mix i could do?
i have also heard that buxus will add ash colour to hair. there must be a lot of ash blondes who want to stay ash out there, but there seems to be no easy solution to keeping ash hair and covering grey. Anthony would make many of us ash blondes very happy if he made up a mixture for us nomicons/smile