Why do miniaturized hairs lose color?

I still have a full crown hair wise but you can clearly see the skin, the hairs are transparent, they have basically no pigmentation and that’s why it looks very thinning. What is the underlying science behind loss of pigmentation in AA? I couldn’t find any studies on the web

Miniaturized hairs often lose pigment and color because the hair follicle production is impaired and continues to get worse as the process progresses. As the hairs get thinner and thinner, they contain less pigment and eventually become clear (see-through) as the pigment cells in these hairs die.  These hairs also often stop growing before eventually falling out completely.