Has anyone tried the loreal supreme dream blonde haircolor kits, and what color was your hair to begin with?

I have blonde highlighted hair on top but its a dark, almost light brown underneath and I was wondering if i colored my hair would it all be the same color(which i want) or would the undermeath be brassy and yellow and the top be blonde, and which one should I use, will the 8 be too dark and 10 be too light? please if anyone has tried these i would love your knowledge!