Girls with brown hair usually look best in greens, blues, and peaches. It just depends on how light or dark your hair is and your skin colour and what not. Try on a few sweaters and see what colour you like best (assuming you're asking for yourself)!
I think dark/ med brown hair looks good next to pink-heavy peaches, teracotta colors and baby blue. You can't go wrong with aqua/turquoise(looks good with EVERY basic hair color and most skin tones) or pale yellow though.