My roots always turn yellow!

grrr. Ok so all my hair is a really pretty light ash blonde color, almost white, but I really like it. It doesn't look all fakey or anything, except for at the root area. I touch it up with this stuff called Blondissimes by Loreal in LB01 Extra Light Ash Blonde. And it works really well, but it only looks good for like a week. After a week or whenever my roots start coming through, the area on top like an half an inch from my roots gets really brassy and yellowy. I even have Shimmer Lights but it doesn't help, it only makes the rest of my hair white and the roots stay yellow so it looks worse. And my natural hair is medium blonde so it's not like I have a bunch of dark roots to dye over. What can I do to not make them do that? Should I bleach them and tone them or something? that just seems like such a pain.

I want it to look like this on top. The rest of my hair is the color here though

this is from before I started dyeing it