All -
I don't think this is due just to blue jeans only. Like many things, there is not one simple culprit, rather I think it is a combination of things.
I have a 1986 Kenmore dryer, which I bought new. It is one of the earliest models with the white finish drum. Years ago it was developing that blue hue, which I didn't like, so I called the Whirlpool help line and asked what was going on. They told me it was due to fabric softener sheets, and film build-up that was getting discolored, not the drum itself.
At that point I quit using dryer softener sheets for many years, and the blueness (which was never as healthy as in the pics above) eventually wore off. I certainly never quit wearing or washing my jeans though.
So, I'd venture a suggestion that fabric softener film has built up on many dryer drum and bulkhead surfaces, then a transfer prone garment such as jeans, new towels, etc. transfer their color to the softener build-up. I think it a lot more likely that softener film could be discolored vs. high-heat enamel.
What is odd is that I have a 1978 Kenmore dryer as well, which has the previous gray finish (what hasn't worn off) and I've never seen any sign of discoloration in it, though it's harder to see. It must be something particular to the white finish that attracts or retains the softener. I think the comments about the venting efficiency are especially smart - higher internal temperatues (due to poor venting) probably would encourage softener build-up.
I suspect a cleaner/polish capable of removing surface stains and oxidation from a car paint would remove the discolored softener film.
I didn't want that blue color in my dryer, and it was all my clothes in there. If that were a dryer I bought used, I'd especially want it gone.
Gordon