Grab a bowl and mix together equal parts baking soda and shampoo. Stir it well so the two ingredients are thoroughly combined.
Get your hair wet with the hottest water you can tolerate. The hotter the water, the more effective the paste, but be careful not to get it too hot or you'll scald yourself.
Massage the baking soda paste into your strands. Work the mixture into your hair well using your fingertips.
Rinse the mixture out well, then condition your hair like usual.
Although baking soda will help to remove the hair color, it's not going to happen in one application. You may have to apply the paste several times before you get the results you want.
After using the baking soda paste, deep condition your hair. Baking soda is slightly abrasive and coupled with hot water can damage your mane. Using deep conditioner will help minimize any damage.
If your hair color is too dark and you want to lighten it a couple of shades, mix a teaspoon of baking soda, a teaspoon of 20 volume peroxide and your regular amount of shampoo. Massage it into your hair, let it sit for a few minutes, then rinse it out. Repeat as necessary until you've achieved the desired shade.