Welcome to health care. Hope you find your answer in this forum.
Well, the symptom that you are telling can be really significant. The points of concern uhere are
1. gender of your child,
2.whether the hypepigmentation(dark skin) is all over the body or started off with some specific parts like the knuckles and the elbows,
3.if it is following any precipitating factor like exposure to sun or ingestion of any drug.
4.any other associated feature like vomiting
, excessive weight gain
I would advise you to see your pediatrician
or if possible a pediatric endocrinologist
at the earliest. Anyways, i will always be available for you, if you have any more querries and need any clarifications. Take care....bye....