Depending on the facility, instructors and lifeguards are required particular colors or uniforms.
Not all swim instructors are lifeguards. Nor are all lifeguards swim instructors.
While at public pools they usually are one in the same: the lifeguards teach swimming. Lifeguards and BSI (basic swim instructors) and WSI (water safety instructors & swim instructors) are certified by the American Red Cross (assuming you are in the USA).
At a private club, I would only hire swim instructors who had WSI qualifications.
Hope that helps,
Kimber (aqua fitness pro)