Mid/lighter brown hair with highlights.. can I colour over it?

[MedusaIsHavingaBadHairday]

The highlights are fine and more 'grey blenders' than strong highlights, as I have a few grey hairs at the front now. However my hair always goes a bit brassy IMO and I'd really like to just have an all over chestnut/ warm brown. I can't afford the hairdressers at the mo and have a an inch of root growth.

Can I do this with a semi permanent over the fine highlights or will they turn some unexpected ghastly colour?

Thanks!

I did and it was fine. Use a semi and pick one lighter than you think you need as they always go darker! Go for a warm shade, not ash and there will be no green tinge!
I use Castings - usually a 600 (neutral light brown) or 603 (a warmer light brown) and only leave on all over for 10 mins - not the full 20 - else the ex-blonde bits take up too much dye and go too dark.
Good luck.