Hey, just posting an update in case anyone's curious.
I took her to the vet today, and the vet...found absolutely nothing wrong. She agreed that the color change was very strange, and has posted it on some vet forums. But everything on her physical came out just fine. The vet's first instinct was that it could be environmental (something in her last meal), or a strange manifestation of her morph. She was confident that it was not hypoxia. They are running bloodwork on her, and I'm going to take in a fecal sample ASAP, but it remains a mystery!