The black pigmentation on legs is post inflammatory.
After mosquito bites, you develop lichen urticatus and prurigo lesions
This is followed by hypermelanosis
First of all, you take all precautions to avoid mosquito bites.
Apply kojic acid
and vitamin C
Take vitamin C and E , take glutathio for long time.
Rub kojic acid containing soap during bath.
I think you would be benefitted.
I hope you got my answer.
Dr. Ilyas Patel MD