When you have high levels of confidence that the background will be ocean water and the weather is likely to be decent (or at least, decent enough to be diving)

When you have high levels of confidence that the background will be ocean water and the weather is likely to be decent (or at least, decent enough to be diving), then it may be the case that yellow is more visible. International Orange is designed to be maximally visible under as many different conditions as possible, so may not be the most visible in every single circumstance.