Why has my hair dye gone wrong?

i have a real crappy natural brown hair colour and always have it highlighted using foils blonde.

I fancied a change now and wanted to dye my hair a nice dark brown b ut because i wasnt completely sure, used a semi-permanent dye as a tester. Having used the semi-perm brown dye over my blonde highlighted hair, i now have bluey/grey coloured streaks where the blonde highlights originally were. why is this? and can i now just put a permanent dark brown dye over the mess i have and be rid of it?

Why has my hair dye gone wrong?

Yes you can--just make sure to make it a neutral tone.

Sounds to me like you used an ash shade of dye and maybe that's why your hair came out kind of greyish. Also, semi-permanent dyes aren't completely absorbed into the hair shaft, so that may have resulted in your weird color.

My advice would be to use a clarifying shampoo to get as much of the dye out as possible, the dye over it with permanent color.