I learned the hard way that boxed dyes just don't work well for me. A few months ago, I tried one that had a pretty name like "soft violet black." Sounds nice, right? What I ended up with was brown hair and hot pink roots. Trust me, it wasn't cute.
Unfortunately, I had to live with it for over a week before I could get it fixed. I could have saved myself a lot of ponytails and humiliation if I'd known then about a quick fix that redditor whatsherface pointed out—Vitamin C.
You can fade hair color by crushing up a few Vitamin C tablets and mixing the powder with your shampoo to form a paste. Massage it into damp hair and cover with a shower cap or plastic wrap. Leave it on for 30 to 45 minutes, then rinse and condition.
This won't completely strip the dye from your hair, but it should lift some of it out and leave you with a softer shade. You can repeat the process a few times to enhance the results. If you don't have any tablets, or just want to skip crushing them, you can also use a powder, and some people have even had success with Emergen-C.
To get an idea of how it works, here's the before and after from beauty blogger Michelle Villett:
It works because vitamin C, or ascorbic acid, works as a natural bleaching agent by decreasing the pH level. It has been shown in food studies to break down the double bond between nitrogen atoms in artificial colors.
Again, this won't take your hair back to natural, but it will help fade the unwanted color in the meantime until you can get it fixed. For more details on the process (and a few other home remedies), check out Michelle's blog.