There is a product by L'Oreal called Effasol [sp?] that mixed with water should remove enogh of the dark color that you can put another lighter shade over it. Since the offending dark color is a "fader" you should only have to use the water, not the peroxide option. You might even like the result without having to color over the remaining stain.
When in cos school, the color instructors used to say that home color products were a boon for the salon. Most people don't read all of the directions included and end up with all kinds of problems. Cha Ching! That said color correction was my fave thing to do in the salon, like a puzzle and when I could make the client happy it made my day!