If the dark part is dyed, another dye color will not lighten it. I dyed my hair black about a year and a half ago. It was auburn naturally. I tried a very dark auburn about 8 months later. The only part that took the dye was the roots. And to make it worse, it seemed like only the reddish part of the dye took, so I looked like Ronald McDonald trying to grow out a goth phase. My hair is also currently long enough to reach the waistband of my jeans.
You can dye it a darker color to cover the red, or you can try to have the color removed. Salons will strip old color, but that’s pricey and I’ve never personally had it done.
I used this stuff called Color Oops (it’s on amazon.com, I also found it at Rite Aid). The bottom of my hair is still darker than the top (which is grown out about 7-8″ now), but it’s a lot lighter. I did it two months ago, and I’m considering doing it again. It does work, though there are a few buts:
First, it smells fairly bad. It’s sulpher-based. What it does is undevelops the color so it rinses out. Some have likened the smell to a flower garden in Hell, though I didn’t find it as offensive as that. But it really isn’t pleasant.
Second, you HAVE TO follow the rinsing directions to a T. You need to rinse for 20 minutes straight, shampoo, rinse for another 10 minutes, shampoo again, rinse again for more time. The more you rinse, the more likely it is to work. People have reported the color coming back because not all of the molecules were rinsed from their hair. At that point, they just re-expand overnight and you’re back to square one. The hot water ran out about halfway through for me, so I was blue by the time I got out 🙂 But I stuck with it. I also used music to time the rinses, and to keep myself occupied 🙂 I picked up a cheap clarifying shampoo to do the job. You want something that is going to strip your hair a bit for this job. I’ve read people using Dawn dishwashing liquid, or Head and Shoulders. I didn’t go with the Dawn because I was really concerned with over-drying.
Third, all of the color will likely not come out, particularly in the older parts. The bottom of my hair is almost black (I dyed it many many times before stopping, plus I’ve been dyeing it for years), but it’s lighter and lighter until it’s basically natural at the top. Also, if it does strip the dye, your hair will likely be a different color than you started with. Permanent dyes have peroxide, so it does lighten your hair during the dye process.
Fourth, it’s not as damaging as bleaching, but all that rinsing and shampooing (plus the fact that it does open the cuticle to let the particles out easier) dries your hair out something awful and makes it look and feel all scarecrow-like. Use a deep conditioning mask-type thing after the rinsing is done. I’ve read that the cholesterol masks found in ethnic hair care aisle works well. I don’t remember what I used, but it worked. I picked it up at the pharmacy, but Sally Beauty Supply has a lot of options. I did have to condition my hair everytime I washed it for about a month (though my hair was already a bit damaged as it is), but I didn’t experience any more breakage than usual.
And finally, they say you can dye it again the same day. BUT this stuff will make the dye take much darker than you’d expect, so if you do it, get something much lighter than you would normally use. I ended up waiting a few weeks, so I can’t say for certain how light you’d want to go. I actually wasn’t going to dye again for a while, but the greys were driving me nuts. I’m off the permanent dye for a while and am only going with semi-permanent when I absolutely need to.
It should take out the red you just did fairly easily. The older dye, it should lighten, but you might need to redo it at some point. They say you can do it again within a few days, but I haven’t yet. My hair was way too dry to begin with.