This question is nothing that a very simple Google search, search on Amazon, etc could not answer -- but yeah, they are out there. Now I don't mean that quite as harsh as it sounds, but if you want to be successful (read not simply an employee to an entitiy within the system) your very thought processes and approach to dealing with things needs to change -- never ask of someone what you can readily find for yourself, never put something that needs to be done off til tomorrow what can be done today, etc.
As to the reason why you mostly see white skin -- demographics and logistics. Skin disease often relies upon subtle clues, color changes, erythema, etc. It can be very difficult to appreciate in person with good lighting, much less in a photograph. Many of these changes (particularly subtle vascular and inflammation influenced color changes) are extremely difficult to appreciate in ethnic skin.
