Final answer:
To correct the yellow discoloration in white hair, a purple-based toner should be applied to neutralize the yellow tones. This type of product is often called a silver or purple shampoo and must be used according to the manufacturer's instructions to avoid dyeing the hair purple. Couplers in hair dye provide color, but toning is the key step for correction.
Step-by-step explanation:
To correct yellow discoloration in white hair, a purple-based toner should be applied. The color purple is directly opposite yellow on the color wheel, which means purple tones can neutralize yellow ones, counteracting yellow streaks in white hair effectively. When performing a color correction of this nature, it is essential to choose a toner with the appropriate shade of purple to match the level of yellow discoloration. Salon professionals often refer to this type of treatment as using a "silver" or "purple shampoo," which is specifically designed to address the yellowing that can occur with white or gray hair. Additionally, it's important to follow the manufacturer's instructions regarding the processing time to ensure that the hair does not adopt a purple hue.
Couplers, such as the ones mentioned like red couplers or blue coupler, are used in hair dyes to define color; however, for correcting yellow streaks in white hair, these are not typically used as standalone treatments. Instead, they are part of the formulation for creating specific hair dye colors. Hair coloring involves a chemical process that can include the oxidation of compounds like p-phenylenediamine to create the final hair dye color. Nevertheless, the main focus for correcting yellow streaks would be on the application of a toner with a purple base, rather than reformulating the hair dye itself.