About Sarracenia specifically? I haven't seen the article you're talking about, only ones about bio-indicators and carnivorous plants are research papers using the plants as bio-indicators of the health of the surrounding environment they're growing in. The leaves wilt when the soil starts to get too dry as well, not just ambient humidity (I've actually never seen them get floppy over low humidity in the air.) Growth will be green and weak, pitchers uncolorful and stunted if they aren't getting enough light, or strong enough light. Temperature will also change the colors seasonally in many Sarracenia species, but that's supposed to happen. Are those the type of thing you're looking for?