Thats subtle. I think it is supposed to look like a vein with some blockage seconds before a stroke.
That 'artist', Kehinde Wiley, is another black homosexual racist pervert like so many of Obama's other associates.
He is also well known for sneaking thinly disguised little spermatozoa into his portraits.
So there is no doubt Obama knew what to expect when he chose Wiley to do his official portrait.
Here are a couple of other examples:
Several images in those backgrounds look like captive heads screaming for freedom.
I think I would be embarrassed to have that painting hanging anywhere but a bathroom.