Obsessed, did you try running a Google search on this question? Lots of stuff out there on things like StyleForum and AskAndy.
I have not had enough time with it to come to any specifc conclusions except that lighter brown shoes (I am talking Cognac or so, I guess not really "tan" unless a dark tan) with a navy suit woud apparently be considered "fashion forward," so I guess my impression was correct that some time ago one started seeing lighter brown shoes with navy suits for the first time in lifetime. Apparently the old British rule was never anything but black shoes wih a navy suit--with actual Brits writing in on this to confrim that their fathers had stated this rule unequivocably, but there is debate over how old that rule is and whether it went away say 80 years ago. (I do not understand where cordovan and oxblood shoes would fit it to that. I thought the rule was that cordovan went with everthing.) But there are Continental Europeans writing in saying they do not like black with a navy suit and wear nothing but brown shoes.
I think your gut and my gut feeling is black shoes with a navy suit is the "rule." My feeling is that it is okay to break a rule for "fashion." It is less okay to break a rule for me just because I think it looks okay. Like lots in life, I want the impression to be that "I know how something show be done and have consciously chosen not to do it that way, rather than I do not know how something is supposed to be done!"
I would say that gray suits are a whole other thing. I am frankly not convinced that blue suits other than navy ones are!
I have not had enough time with it to come to any specifc conclusions except that lighter brown shoes (I am talking Cognac or so, I guess not really "tan" unless a dark tan) with a navy suit woud apparently be considered "fashion forward," so I guess my impression was correct that some time ago one started seeing lighter brown shoes with navy suits for the first time in lifetime. Apparently the old British rule was never anything but black shoes wih a navy suit--with actual Brits writing in on this to confrim that their fathers had stated this rule unequivocably, but there is debate over how old that rule is and whether it went away say 80 years ago. (I do not understand where cordovan and oxblood shoes would fit it to that. I thought the rule was that cordovan went with everthing.) But there are Continental Europeans writing in saying they do not like black with a navy suit and wear nothing but brown shoes.
I think your gut and my gut feeling is black shoes with a navy suit is the "rule." My feeling is that it is okay to break a rule for "fashion." It is less okay to break a rule for me just because I think it looks okay. Like lots in life, I want the impression to be that "I know how something show be done and have consciously chosen not to do it that way, rather than I do not know how something is supposed to be done!"
I would say that gray suits are a whole other thing. I am frankly not convinced that blue suits other than navy ones are!