After I wrote about the Levi's stitching thing recently, I was able to return them to a store (I'd ordered them online, which is why I didn't know the stitching color had been changed), where I found that many of the other shades the 505 is offered in have also had their stitching changed.
Disappointed, I returned them without exchanging for another pair. I wasn't sure what I was going to do; I thought I'd start by checking eBay for older pairs that hadn't been worn. But before I had a chance to do that, I happened to go to a Kohl's with the Mrs., who was looking for a piece of luggage small enough to take on planes.
I checked their Levi's too, but then I noticed that right next to them on the same wall were the store's house-brand jeans. The label said "regular fit" and they were clearly meant as an alternative to the 505. I had thought this particular brand was made only in "young men's" styles and washes, so I figured it was worth trying them on.
They fit exactly like 505's, and they're available in the same "dark stonewash" shade (which looks quite a bit lighter in the online image than it is in real life) that I've been buying for five years or so. (I have no interest in elaborately distressed washes or selvedge denim; the basic stuff works just fine for me.) And the best part is they have a "regular" price of $36 and are typically available for $20, which is half the cost of a pair of 505's.
I wasn't looking for these, but I'm glad I found them. I'll have to see how they hold up to wearing and washing; I'll post an update in a few months.