Little bit of yellow sick

Hi im wondering if anyone can help me. I have a 6 day old baby and this monring she has been sick a slight bit of bright yellow before throwing up what seemed like the whole contents of her bottle. The yellow part was enough to cover one side of a scratch mitten so it wasn't a lot but it was quite bright. She has had another bottle since and not done it again I'm just really worried. I have phoned the hospital and they have said it seems quite normal but I've heard that yellow sick is bile?? Can anyone help or give me some advice or has anyone had the same? Thanks very much 😔