There are a number of companies that make permanent purple hair dye, including Vidal Sassoon and L'Oreal Feria. These products are available at many online retailers as well as neighborhood drug stores.
Although permanent hair dyes do permanently alter the color of hair, the color that is achieved immediately after dying eventually fades. This is particularly true of high-intensity colors such as purple. To maintain the color as long as possible, start with well-prepared hair, and take care to keep it in good condition. If the hair is dark and a true bright violet color is desired, the hair needs to be lightened before applying the purple permanent dye. To minimize damage, apply a deep conditioner daily for several days before coloring the hair. As closely as possible, follow the instructions included with the hair dye. After dying the hair, wait several days before shampooing it. Use only products intended for color-treated hair, and look for products that do not contain sulfates. Sulfates can strip the color more quickly, and they can also damage hair that is already stressed from being colored. Ensure that styling products do not contain alcohol, which can also strip color and damage hair. Finally, ultraviolet light also fades dyed hair. Avoid the sun as much as possible, and make sure to use products designed to protect the hair from UV light.