This is probably starting to fall into the category of too much information, but in my case I think it's likely from peeing out in the woods and not getting perfectly dry down there afterwards. Definitely not menses as I'm spayed.
And the color isn't that
But it also falls right in line with that large seam in the front of my jeans. So it is probably a combination of excess moisture and the seam causing friction.
A little too much information but since we are going there in the discussion anyway, well, we might as well!
When I only owned dark saddles I never had a noticeable spot at all. But with a medium oil saddle, well, there is a little bit of a darker spot starting to show up.
No matter what the cause, I would guess most saddles, after many years of use, will have some kind of wear and discoloration to the seat. Whether it's from the rider's jeans, sweat, a little excess moisture after getting off to pee, etc. It's almost inevitable.
A seat saver may be a good idea. I used to use fleece ones just for comfort. But I've gotten to like a slick seat saddle now so it's hard to put stuff between me and the seat.
Does anyone have a light colored seat that does NOT have any wear marks after years of use? Unless they use a seat saver I would think not.