While most cats are able to vomit up hairballs without any issue, there are some occasions when the color of your cat's vomit can be a cause for concern. If your cat is vomiting up green or yellow bile, this could be a sign that they are suffering from liver disease. If the vomit is red or contains blood, this could be indicative of an intestinal blockage or another serious health problem. In either case, it's best to take your cat to the vet as soon as possible for further evaluation and treatment.