This popped up rather suddenly on one of my Nepenthes. It doesn't look like rust to me, but could it be some other sort of infection? There's a pitcher several leaves above this that finished growing a week or two ago but never opened, and now I'm seeing the same brown pattern on that leaf as well.
I also noticed that the new growth since I rooted this cutting is very yellow in comparison to the old growth which I'm quite sure was not the case several weeks ago. You can also see some of the older, much greener leaves in the first picture. I don't think the difference is quite as much as it looks in the picture though, it was hard to get the white balance right.
Any help would be appreciated!