Since you want brown highlights, you'd have to get your hair to an orangey state, then, you'd have to tone the highlights with a blue based ash color (since blue cancels out orange).  If the brown color you want is on the darker side, then you'd probably only have to lighten your hair to a reddish state, then you'd need to use a green based ash color (because green cancels out red).  Try using a blue based shampoo as well, once a week or so, so that you don't get the brassiness. 

 

I myself have given up on making my hair lighter.  Since I chemically straighten it, I rather not bleach it because it will really damage it.  My only option is to use a 20 volume oxidizer.  My last try (which was a couple of days ago, at a salon) was the Redken Color Fusion in 5AG (ash green), my natural haircolor is a number 4, so I was only going one shade lighter.  Needless to say, my hair is now orangey, it simply doesn't work.  I've come to terms with my hair, I've realized I'll never get an ash based brown, period.  Unless of course I was to bleach my entire head pale blonde and then tone it.

 

I don't understand why they say olive skin tones match with warm colors, that's a bunch of B.S.  At least not for my hair, warm colored clothes do look better on me, but when it comes to hair, it looks like crap.  Go figure.  I'd like to know who's the colorblind stylist that came up with that. 

 

Good luck with your hair, I really hope you get the color you want, I'll even pray that you do.  Let us know how it turns out.