Steel Gray Hair Color
A: Finding a "steel gray" in a permanent hair color is not going to be easy, except among the more costume-oriented colors.
What you want to do is use a color similar to your natural color before you went gray and have finely distributed lowlights applied using that color to give you a darker look. You may even go slightly darker in the lowlights for a deeper color.
A good colorist can help you create a natural pattern of lowlights to give you a natural looking result. Just remember that when dealing with unpigmented hair, you need to have a lot of variance in the color in order to prevent a flat-looking color. If this proves too costly or time consuming a proposition, you might consider trying the temporary rinses to get the color you want.
The most prevalent brand of temporary color rinse is by Revlon. It is Roux Fanci-Full Color Rinse.
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See also:
How to color hair
Temporary hair rinses
Is blue rinse for gray hair not made anymore?
Can I color my hair steel gray with a semi-permanent color product?