Once upon a time, Penang was a hub beween the UK and Hong Kong. During the war, various battles were fought in the Straits of Malacca and later it was a submarine base for the Japanese. These days, the harbour mostly handles cruiseships and ferries carrying holidaymakers to Langkawi (which I will probably write about another time).
When I lived there, once a week, I would try to walk from my home to the ferry terrinal. Some days, it would be fiercely bright, making the sea look a light blue and on other occasions, thick clouds would appear and the sea would take on a greener hue (like here).