To get vivid blue hair, start by bleaching the hair with a soap cap until it's pale yellow. Apply the blue dye, allow it to process, rinse, and remove remaining pigment with shampoo labeled for color-treated hair.
- Mix a soap cap
In a plastic bowl, mix equal parts lightening powder, developer, shampoo and distilled water. If your hair is medium-to-dark brunette, use 40-volume developer. Use a tint brush to mix the soap cap.
- Apply the soap cap
Divide hair into four sections. Apply the soap cap to 1/2-inch sections of hair with the tint brush. Start at the mid-shaft and work down to the ends. While wearing protective gloves, work the mix through to the scalp.
- Process and rinse
Cover the hair with a plastic bag, and allow the hair to process until it is pale yellow. If starting with very dark hair, it may be necessary to apply external heat. Wet the hair to activate the shampoo, and rinse until the water runs clear.
- Protect the skin
Because blue hair dye uses strong pigment, apply petroleum jelly to the skin around the hairline. Wear gloves when applying and rinsing the hair dye. Drape yourself with an old towel to prevent the dye from dripping onto your clothes.
- Apply the hair dye
Mix the hair color according to the manufacturer's instructions. Apply the dye evenly over 1/2-inch sections of hair. Work it through each strand to ensure even color coating.
- Process and rinse the color
Leave the dye in the hair for the recommended amount of time. For more vivid tones, leave it in longer. Rinse with cool water, and follow up with shampoo for color-treated hair.