Most U.S Navy, and other nations ships, are painted 'haze grey' to make them less visible.
It seems that the Iranians missed this subtle difference and want their 'great' submarine to be seen.
When it is submerged, it doesn't make any difference what color the ship is painted. Ever see the movie Operation Pink Petticoat?
The boats are painted according to their mission. There are about four major colors for submarines--light gray, dark gray, blue, and green. One of the colors is light green: where would that one be stationed?
It's green camoflage to blend in with the forest......