6 week baby spit up has a little yellow in it ??

[Dbf123]

Hi my 6 week old baby had a little bit of spit up whilst winding and some of it had a little yellow in it has anyone experienced this befor ? Added a picture

Forgot to add that baby is well in self it was after a 4 ounce bottle she never vomited just a tiny bit of spit up and was quite settled after

Could be just curdled milk, bringing up bile having milk on empty stomach, obviously if it continues ring 111 for advice.