Dark spots on my baby's back

My son has these 3 darker spots on his back. They're no dry or flaky, don't seem to be bothering him. He's had them since he was born. Should I be worried about them?

My husband does have vitiligo on his hand but the spots are lighter, not darker. Maybe it's some form of hyperpigmentation?

EDIT: there's actually 4- 2 smaller ones on the side, the larger on on the other side and a tiny one in the middle.

I only noticed the 2 smaller ones before then my husband noticed the bigger one and showed me. I just noticed the small one as I was posting this.