... interesting and intriguing issue. I´m inclined to think without being an expert that exposition to light and sun tends to a light patina. May be I´m biased by my experience with my own 1680 which is acompanying me as an almost only watch from 1977 till around 2008 in which I begun collecting watches and switching watches in almost daily basis. I still wear it from time to time of course. This faithful 1680 was used in sport scuba diving, beach, pool, daily work at office, worn day and night while sleeping and taking a shower. It became vintage together with me and patina is now a pale cream. The bezel turned nicely faded too. Please see photos below. By the other way, I have seen Submariners with a very heavy patina but having the case interior and movement pristine I would discard the influence of humidity in the formula of a heavy patina. An example is my Tudor Ci, which I am sure had a very hard use during its military career (which most probably included good exposure to sun light too!), and has a much darker patina. Again, interior of case and movement do not show any trave of corrosion by humidity. So, firm conclusions are really hard to reach. Thank you again Bill!