First time hair colour- unhappy

Going darker is generally easy, but you need to be a bit careful when your hair is very light. If it has very little or no red pigment, chances are it will turn green-ish. If it has an orange base however, you might be fine, but I'd still recommend doing a test strand just to be sure.

If your highlights are very blonde, you need to 'fill' them with a red-based color before using a brown dye on top. Also you need to be careful with how dark a dye you choose, as bleached hair often grabs color more than natural hair does, and box dyes tend to be darker than they seem as well. Again, test strand just to be on the safe side!

Box dyes also tend to have a lot of red pigment in my experience - when I had dark hair it was quite the battle to keep the red glow away! You might want to go with an ash color to keep that at bay. If you have a lot of reds in your hair already, it will cancel out the ash tones and leave you with a neutral color. However, it's a little hard to be sure with box dyes as you don't know exactly how much pigment of each color is in, but generally dark brown is easy to achieve nicely at home.

So, just how light are your highlights, and what color do you want them to be? 🙂