Usually, the first cycle of hair regrowth with alopecia areata is gray and very thin but the next cycles make it thicker and healthier.
It has been found that alopecia initially targets pigmented hair and then non-pigmented.
“Alopecia areata has been compared by some to vitiligo, an autoimmune skin disease where the body attacks melanin-producing cells, leading to white patches. Research suggests that these two conditions may share a similar pathogenesis, with similar types of immune cells and cytokines driving the diseases and common genetic risk factors”
” Regrowth may initially present as fine and non-pigmented hair, but usually the hairs gradually regain their normal thickness and color. Regrowth in one region of the scalp may be associated with expanding areas of alopecia elsewhere”
My personal experience demonstrates it completely (2 patches above the neck). The recovered piece of hair was thin and gray, even white as children one and then got back to its’ original state.
But I saw a person whose hair color on the forehead hasn’t been recovered from alopecia happened 20 years ago and was thick and dense but gray.
So I guess it varies from person to person.