If your hair is dark and you use the lightener, it may turn out orange (I know by experience!) - it depends on just how dark it is. However, if you put light brown straight on to the bleached hair, you may find it turns a lovely sage green (again, known by experimenting!) You need to introduce some shade of red back in before putting on brown.
May I suggest you cut off a lock and enjoy experimenting to see how the dyes affect your hair before committing to any extreme response from others not so adventurous e.g."whatthehellhaveyoudone?"
I'm far more careful now about how I introduce colour to my barnet!!
Good luck
Debs