here is why you dont want to expose your sea wolf to a lot of sun! see ebay ##330574083769. it is a "tropic dial" for sure. the black ones turn spotty brown also. i am afraid i just dont want "patina" on my watch dials!!!

There was likely a little moisture involved in the changing of that dial as well.  One cannot know without seeing the movement, but I would guess that it has atleast a small amount of rust on the movement, which does not come from one moisture exposure.  Any moisture in the case, if given enough time, will gravitate towards and change the finish of a dial and the luminous.