If you are color blind you should still be able to work as a paramedic. However, some Ambulance Services require that you meet a certain criteria if you are color blind. As a general rule, if you are legally allowed to drive a motor vehicle in the state that you want to work, you should be allowed to drive an Ambulance as a paramedic.
However, some Ambulance Services still maintain a complete block for persons who are color blind (on the erroneous belief that they will misinterpret traffic lights, even though, this is not the case for most persons who are color blind, and not at all the case for any person who is color blind, but meets the standards to drive a motor vehical under state laws.
If you fall under this category, and the Ambulance Service that you wish to work for refuses to accept your application on the basis that you are color blind, I would recommend that you argue the point that this is descrimination under the Equal Employment Opportunity Act (in Australia) and that, unless they can prove how this disability directly affects your ability to do the job, they are legally bound to offer you the same chance of employment as anyone else.
If you still have no luck here (and can’t afford a lawyer) and you still want to be a paramedic, I’d recommend looking into another Ambulance Service, because most of them now accept paramedics who are color blind.