Bile is usually green or yellow, in
experiences. If it was white and foamy, it could be frothy mucus
...hard to really say.
If it was a one time thing, just watch him carefully for other signs of distress such as abnormal panting, unusual behaviors such as rolling repeatedly or getting into the "praying" position often, diarrhea, not eating, or if he seems to be biting or bothering at his flanks, or tummy bloating.