I’m not sure if my experience is what you are describing. My silver minipoo had a bee sting on her paw last summer and had a dose of allergy medication and I limited her ability to lick her foot for a few days.
I noticed the next time I groomed her where the bee sting occurred she had a black spot. When I looked closely I realized she had alopecia - no hair was growing, the black was her skin. I groom her feet every 2-4 weeks so I don’t remember the details, but the next time I groomed her feet I discovered inky black fur was growing. For several grooming sessions she had black fur growing normally next to her normal light silver. Eventually over time the black faded to her regular light silver. This summer she got poked by s sharp thorn on her back and it’s growing back black and will eventually fade to normal silver. Once the hair fades it will be indistinguishable from the rest of her hair.
If you search bee sting, I posted about it with photos and updates.
Babykins CGCA, TKP, ACT1, BN, CD, SCN, SIN, SBN, RN, AKC Achiever Dog,TDI (Therapy Dog International)
WCRL Rally titles: RL1, RL1X Award of Excellence, RL2, RL3
AKC CGCA=Community Canine Good Citizen, TKP=Trick Dog Performer+Novice+Intermediate+Advanced) ACT1=Agility Course Trial 1, BN=Beginner Novice Obedience, CD=Companion dog/Novice Obedience, SCN=Scent Work Container Novice, SIN=Interior Novice SBN=Buried Novice
C-Wags title -Scent Patrol Level 1, Scent Detective Level 2