My hair is turning gray. (The color is only called grey when it describes a horse.)
Recently I examined two samples of cut hair, one from the end of a cubit-long ponytail, recently cut off; the other from six-inch sideburns of the same vintage. Like a horse, I am graying from the nose to the tail; in this case, from the temples to the nape of my neck.
Least gray hair: Munsell 7.5 YR 3/4 in Daylight-Equivalent Illumination
Grayest hair: Munsell 7.5 YR 5/2. The hue stays the same, but tone lightens and saturation decreases, as one would expect.
The illustration shows ponytail and sideburn hair and Munsell color chips, as taken with my scanner. The scanner's illumination is not the same as Daylight-Equivalent Fluorescence (the standard for using Munsell color chips), so the color match may not seem accurate.