[PPPE-255] Encouraging Lesson in Positive Affirmation and Lewd Talk: Deflowering by a Shotacon Busty Tutor, Yuzuriha Karen

The second most likely answer is lighting differences in different scenes.
Third most likely answer is different cameras having different color profiles, and porn producers not caring enough to recalibrate for high fidelity color reproduction.
Fourth most likely answer is she changed her birth control. Different birth control pills use different combinations of estrogen and progestin (progesterone) to trick the ovaries into thinking the uterus is occupied with a fetus, which can have varying effects like darkening linea nigra, nipples, and vulva, even breast swelling and new hair around nipples.
Fifth most likely answer is that she just hasn’t had her nipples bleached as recently in this film, and they’re returning to a natural color slowly.
But the most likely answer is… they aren’t. You’re imagining it. I just pulled up JUFE-271 to compare to 3.5 years ago, and they’re pretty much the same. Any miniscule differences between her nips in PPPE-255 and JUFE-271 can easily be accounted for by the aforementioned lighting and camera color profiles.