In Tangier you have two different type of taxis. The grand and the petit taxi. The grand taxi you will recognise because they are usually beige Mercedes sedans. These are the taxis that can take you for a tour around the area. Make sure to negotiate before you step in.
The smaller (and cheaper) taxis you will recognise by the blue color like you see on this picture. Keep in mind these taxis are not allowed to leave the city. When you want to take a ride within the city this taxi is perfect, but when you want to take a tour to get to other cities you will need to take a grand taxi.