What color are all naval mine casings painted?

The correct choice is that all naval mine casings are painted gold. This specific color is utilized to help designate mines visually and provides a consistent recognition factor across different marine environments and conditions. The choice of gold, in this case, stands out within naval operations, allowing for easier identification by personnel who are trained to recognize various ordnance types.

Contrastingly, other colors such as green, silver, and black do not serve the same specific purpose in the context of mine identification. Each of those colors might be used for different types of ordnance or military equipment, but naval mines have a standardized coating in gold to ensure that they can be effectively identified while adhering to military visibility standards.