(Not What You Think) 18th February 2021
Hmm....If you have previously heard of explanations on why submarines are black, well, you need to watch this video. It's not what you think!
(Wikipedia) In early 2006, HMS Torbay (S90) was the participant in an experiment in the use of colour schemes to reduce the visibility of submarines from the air. The standard black paint of Royal Navy submarines was replaced by a carefully selected shade of blue. This was the result of research that found that black was the worst possible colour for a submarine attempting to avoid detection from the air. This change is in part the result of the changing nature of Royal Navy commitments since the end of the Cold War, with Navy operations moving from the murky waters of the North Atlantic to the clearer waters of the Arabian Sea and the Indian Ocean.
^ HMS Torbay (S90) at periscope depth when she was painted blue for trials
Torbay's blue didn't stay long. She reverted back to her original black and was eventually payed off in 2017.