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Use purple shampoo if you notice yellow tints in your hair, and silver or gray shampoo when the color starts to fade. Get your hair wet, then apply the shampoo. Leave it in for the time recommended on the label (typically 5 to 30 minutes), then rinse it out.  Leave the shampoo on for only 5 minutes the first time that you use it to get a better idea of how strong it is on your hair. An alternative to purple shampoo is blue shampoo. It is better suited to silver or gray hair, and may even be labeled as such.  You can purchase color-depositing shampoos as your local beauty supply store. If you use color-depositing products too often, you might end up changing your hair color. Use your color-safe shampoo/conditioner once or twice a week. Every 2 to 3 weeks, use a color-depositing shampoo/conditioner.  For example, using purple shampoo too often, such as every day, can make your silver hair look like it has a purple tint. Don't be afraid to use different kinds of purple shampoo. There are ones that are more like purple dye, and ones that are more like shimmery conditioner. You can even mix them together to create a unique blend. These products wash out, so you should apply them to your hair after you have finished washing it, while it is still damp. Rub the gray or silver rinse into your hair, then let it air dry or speed the process up with a hairdryer.  This product can stain. Use an old towel when towel-drying your hair. If you don't find the applicator bottle convenient to use, try a spray bottle instead. It would be best to do this at a salon, but you can do it yourself. If you are doing it at a salon, consider getting it done at the same time as your root touch-up. If you are doing it yourself, use a low-volume developer and a white or platinum toner. You can also do a bleach bath every 1 to 2 months. Get it done professionally at a salon, and be aware that it can be damaging. While the time between root touch-ups varies based on how quickly your hair grows, for most people it will be somewhere between 4 to 8 weeks. Since this requires a precise hand, it would be best to get it done professionally at a salon. If you cannot afford this, consider getting a friend or family member to help you. If you choose to enlist a friend or a family member, make sure that they have some experience with bleaching and dyeing hair.

Summary:
Use silver, purple, or gray color-depositing shampoos. Alternate between color-safe products and color-depositing products. Use a temporary gray or silver rinse to even out your hair color. Do a toning treatment if color-depositing products aren't enough. Re-touch your roots when they start to show.