That's my nevus flammeus🔥, better known as port-wine stain🍷. It's a harmless capillary malfunction in the skin. The fine blood vessels that run below the epidermis are increased and widened, which causes the reddish color. It's already present at birth. In most cases, it's linked to a somatic mosaic mutation with exchange of a base pair in the GNAQ gene🧬. Mosaicism is a condition in which a single organism possesses more than one genetic line. Getting rid of it wouldn't be a problem these days. But I like the feature!✌️