Okay, so a couple of weeks ago I decided to dye my hair like a mid brown chestnut colour. My hair was like a light brown before so I didn't think it would change it much. But after I had finished dying it my hair was bright red! I have tried dying it again with a light brown but it won't go over the top of it. I used to have very very blonde hair and then did it brown and it worked brilliantly and the results were great, but now after dying it again its gone this horrible colour. Please can anybody help me on how to get it back to a light brown?:(

Since you tried to use a brown and not a red, I have to assume that your hair is naturally fairly dark. Single-process haircolorings use hydrogen peroxide (aka developer) to lighten the hair. Simultaneously, they deposit artificial pigment to generate the final color.

Hydrogen peroxide is definitely limited in its ability to lighten. As it lightens, the hair goes through a bunch of colors as shown in the following link (from RobertCraig.com).

http://www.robertcraig.com/php/pics/shades.jpg

If you want to get past the red or orange, you have to use hair bleach. (Although some may flame me and say that it isn't true, it is. There are many products that claim not to be "bleach", but if you look at the ingredients, they contain "persulfate" -- and all persulfates are hair bleaches). Once you bleach past the red, you can do something else to the hair to get it the color you want.

The problem with that is that you'll often end up at least a dark blonde. If that's not what you want, then you're at an impasse. In addition, even if you dye it back to a darker color, it will often fade to a dark blonde, or even lighter. (A lot of people end up liking the look, however, and opt to keep it).

The other possibility was the "light brown" you mentioned was because you already dyed your hair. If your hair was already dyed, then you're trying to violate one of the "rules" of haircoloring: "Color won't lighten color". In other words, a lighter hair dye won't lighten hair that's been dyed with a darker hair dye. There are a lot of reasons for that that I won't go into (unless someone asks). In this case, you need to remove the artificial pigment in the hair before trying to lighten it further. The way to do that is to use one of the following:

ColorFix, Color Oops, Color Zap, Color Charm Color Corrector, Igora Phantom.

There's another one, but I forgot its brand name, so this will have to suffice. There are a few color removers, like Effasol (L'Oreal) that are simply bleaches. They'll be very hard on your hair, so I don't recommend them. Here's a link (also from Robert Craig) that tells how to use ColorFix so you can get an idea of what you need to do.

http://www.robertcraig.com/php/index.php?location=colorfix

You'll have to explain more about about *exactly* what you did to your hair if you want more ideas or recommendations.