You're encountering a common problem that is, in my opinion, poorly understood.
Whenever you use a single-process haircoloring
, you use hydrogen peroxide. Hydrogen peroxide performs two functions. It lightens
natural pigment (regardless of the shade of the dye -- it lightens the natural pigment even in ultra dark, black shades) and it develops
the artificial pigment that is deposited in the hair. The color companies put lots of shades of colors on the shelves. They do put panels on the side that say, "if your hair is this color, this is the color you will expect", but not many people look at them. Even when they do, there's still the thought that their hair might possibly become a bit lighter if they use a lighter shade. This is, unfortunately, not exactly the case. (I also believe that the side panels are a bit too optimistic in some cases -- and they don't show the orange that results).
Artificial haircolor fades because the artificial pigment that was deposited in the hair, dissolves and is washed away. Most of this occurs when you shampoo. You're now at the stage where a lot of the color has faded. The lighter hair you're seeing is due to the lightening of your natural pigment by hydrogen peroxide. There is still artificial pigment in your hair. The rest of the artificial pigment is quite firmly embedded in the hair shafts and most likely won't come out anytime soon.
Hydrogen peroxide is limited in its ability to lighten hair. As dark hair lightens, it turns red, then orange, finally yellow and eventually pale yellow. How light it gets depends on the initial shade. In your case, it's unlikely to turn much lighter than red -- maybe with a little orange tint. This is true regardless of the shade of the color that you use.
The second problem you're going to run into is that single-process haircoloring won't lighten artificial pigment that is already in the hair. The hydrogen peroxide in the dye "developed" the artificial pigment and there's no way that it will lighten it. So, if you really want to go lighter, you have to remove the artificial pigment. This is done with products such as ColorFix, Color Zap, Color Oops, and Igora Phantom. Hair Color, Hair Care and The No More Bad Hair Days Kit by Robert Craig Salon Products, Ltd.
So, what's the bottom line? You're going to have trouble whether you try the light auburn unless you remove the existing color (artificial pigments) first. Also, your hair will probably become more orange if you try and even if you do use ColorFix.
The actual "fix" is to bleach the hair past the orange stage, but since you already said you don't plan on bleaching your hair, I guess I have no suggestions for you.