A little blood in the vomit is usually nothing to worry about. This may happen when the force of regurgitation causes tiny tears in the blood vessels lining the oesophagus. Your baby's vomit may also be tinged with red if he has swallowed blood from a cut in his mouth or a nosebleed within the last six hours. But do call your doctor if your child continues to have blood in his vomit or if the amount is increasing. The doctor will probably want to see a sample of the vomit if it contains blood or bile, so, although it may be an unpleasant task, you should try to save some.
Green bile can indicate that the intestines are blocked, a condition that needs immediate attention.
Persistent forceful vomiting in a newborn within half an hour of eating. This may be due to pyloric stenosis, a rare cause of vomiting that is most likely to begin when your baby is a few weeks old but could show up at any time before he reaches four months. The baby vomits when a muscle controlling the valve leading from the stomach into the intestines has thickened so much that it won't open up enough to let food through. The problem is simple to remedy with minor surgery, but it does require immediate medical attention. Try not to worry too much.