Follow these two simple gray-be-gone rules:
- When applying Stain Guard, be careful to avoid getting it on any grays at your hairline. If those grays have any bit of Stain Guard on them, the color won't be able penetrate your hair.
- Start your color application with the most resistant gray areas first, even if you're doing a full color. This is normally the very front of your hair, or along your partline. Applying hair color to these areas first will allow those areas to process longer, providing more time for the color to really penetrate the hair and cover up those grays.
Did you do both of these things and still didn't get the coverage you were looking for? Let your Colorist know, and they can increase your developer strength or processing time, or even make adjustments to your blend to achieve better coverage.