Thanks for your history and the photograph.
This is called a port-wise stain, a type of hemangioma which may get resolved by the baby is 4 yours.
Occasionally an active treatment is local sclerosant injections may be useful.
This is important as the spot is on the back of the neck and may need to be treated if it comes on the resting point on the pillow on sleeping.
I would advise you to consult a Pediatric Surgeon to get more insight into the issue.
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