Requirements to be a Navy Corpsman (Hospital Man)?

I am interested in being a Navy Corpsman. The idea of being able to help people from dying interests me more than the killing of them. It seems like an important job and one that could help many. But what are the requirements or qualifications? Does one just enlist in the general category of hospitalman and hope to be made a corpsman. Is it possible to crosstrain as one? I did not pass my color test. I passed my depth though. Does this disqualify me? Any advice or personal insight from former or current navy corpsman. Thank you. I appreciate the time spent.