There are at least six theories. a) Its original Hebrew/Biblical name meant 'Sea of Reeds', so it is possible that the name should really be 'the Reed Sea'...ie 'red' is just a mis-spelling. b) It may relate to a surface reflection of the pink-coloured coral which is common there or c) to a sort of algae that appears on the surface from time to time. d) There is some suggestion that it comes from the water's colour when seen from the eastern side at sunset and e) that it is a reflection of the red-tinged mountains that border it. f) Finally, there was reputedly an ancient King Erythrus who ruled territory nearby and 'erythros' in Greek means 'red'. Take your pick!