Final answer:
To lighten natural black hair by three shades, start the color application from the mid-lengths to the ends, then apply to the roots after some time to ensure even coloring.
Step-by-step explanation:
When lightening natural black hair by three shades, a stylist should follow a specific process to ensure even lightening and prevent unnecessary hair damage. Typically, the hair color application should begin from the mid-lengths to the ends of the hair, staying approximately one inch away from the scalp. Heat from the scalp can cause the product to process more quickly, resulting in uneven color if applied to the roots first. After the mid-lengths and ends have been processed for a specific amount of time determined by the product instructions, the color can then be applied to the roots to achieve a uniform result.