This could happen for a variety of reasons. Here are some examples and what you can do to help prevent this.
- A shade might have been used that was too dark for the target level.
- Try a shade that is 1 level lighter next time.
- The color may have not lifted the natural level as light as their usual permanent color.
- Root Perfection can lift 1-2 levels so setting realistic expectations is important.
- The color may have overlapped onto the previously color-treated hair.
- Precise application on the regrowth-only using the bowl & brush will help prevent this.
- The color processed for too long.
- Aim to complete the application in 5 minutes. Process for 10 minutes. The color may process for an additional 5 minutes if the gray is very resistant. However, do not process longer than 15 minutes as the color will go darker than expected.