You have blonde highlights in your hair but they look grey what should you do?

(I am white female age 40) I had my hair colored a deep black for quite a long time - 7 weeks ago I had blonde highlighted put on the top and looked great - looked brown instead of blonde blonde which was fine - kind of a contrast with the bottom still black

Yesterday I had my hair colored again and stylist used a thicker blonde and now my top looks to be GREY - as far as I know it was the same blonde color

(but I could be wrong)

How can this be fixed??????? Can she recolor the top with another shade possibly without majorly damaging my hair??