Yes, a cool toner does help roots look better! I only apply my toner for a very short time with 10 developer, but it still lifts my hair a noticeable (but not largely noticeable) amount. So I still see them, and they're still brown, but they seem to blend better. My natural hair is very ashy too, so it was a pleasant surprise when I toned my roots with the rest of my hair and the roots didn't go even ashier. Just better looking.