In full sun situation, the mouth will turn solid deep red while the petiole remains green!
These are cool and interesting plants that are not hard to grow, but they do have special requirements. Please do a bit of research before you decide to purchase.
Care in a nutshell is; full sun/bright light, best in a south-facing window, rain water, distilled water or RO water and special soil mix. The key to success is to replicate the environment that these grow in naturally. Winter dormancy is required.
The International Carnivorous Plant Society provides excellent information.