When vomit is bright yellow or greenish yellow in color, it means that the vomit contains bile, a substance that is secreted by the liver, according to Parents. Yellow vomit in babies can be indicative of a birth defect that causes an obstruction in the gastrointestinal tract. It can also indicate a twisted bowel or a blockage of meconium.
Bile-stained vomit is a medical emergency, warns Parents magazine. Babies vomiting bright yellow should be taken in for immediate evaluation. Although a twisted bowel or a meconium blockage is usually diagnosed during a baby's first month, children of school age can develop twisted bowel if they are congenitally predisposed to the condition.