Holy Night Gifter black tights - A stain monster?

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Has anyone had staining problems with the black tights from Volk's white Holy Night Gifter set?

 

I've had my pair soaking 24-7 for nearly three weeks with a change of water and washing detergent every 12h or so. At first the water was almost black every time I changed it but now it's a deep purple. Not so sure I'd want my girls to wear those tights. Guess they'll be safe to wear by next christmas if I continue to soak them.

I had one of my girls in that outfit for about three weeks over christmas but I had one of the coolcat body suits under. I did notice a lot of black fibers on the suit when I took the tights off but no stains at all on her legs.

I had my doll wear a body stocking and thin socks over that before putting on the tights. No stains. I don't remember if I washed the socks since I got the set last year...