Why was the Red Sea named as such?

Back in the 5th century BC, the ancient Greek scholar Herodotus called the sea "Eritrean," translated from Ancient Greek as red. 

 

One hypothesis claims that the name refers to the algae Trichodesmium erythraeum, which is rich in red pigment. 

 

But some scientists believe that the name corresponds to the southern direction, which symbolizes the red color.