Gray Hair and Highlights

A: If there is a specific pattern of highlights you want for your hair, in addition to covering the gray you have, then you will need to have your hair highlighted separately from the over-all coverage.
In order to do this, you need to use a shade of hair color that will work well with your natural color (with a similar base color) and is at least 3 shades lighter than your natural color. This will cover the gray, but leave it light enough to be distinguishable from the darker hair.
The second stylist was obviously thinking in terms of giving you gray coverage, along with highlights. You can get the desired effect through foiling, where the stylist will apply highlighting color to certain segments of hair and covering them with foils, while applying the base color to the rest of the hair.
The process you choose depends on the results you desire. If you simply want gray coverage that looks very natural, then you simply need one color applied. If you want specific highlights, you need to have two colors applied.
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See also:
Color hair
Gray hair Q&A
The implications of going gray