Haven't been in here for quite a while.
To be honest, I'd tend to believe that it is in fact florecent lighting that "fades" the color on these shoes. I'm no expert but mine were almost surely a "floor" model (bought on fleaBay) and I think they must have spent a good part of their early life under store lights. I do like it but I'd hate to say sunlight does the trick and have someone ruin a beautiful pair of shoes unknowingly.
Maybe someone wants to take a photo of your shoes in an exact location (and time of day/lighting), then leave them out as long as possible between wearings at say, your office, under florecent lighting and then take another photo to match the first. Maybe settle it once and for all. I can't help as mine are already so light