So I noticed that Boa, before she died, had black eyes like a shark. all the time. I thought that was just her eye color. Now I've noticed that Mamba's eyes, who are usually pearly white with a black pupil, have started randomly turning black and then back to normal. Its pretty weird. I've googled and googled and no one has a definite answer other than the fact that it does happen. Some ppl have speculated it is stress. That makes sense since I don't think Boa was well any way before she got into the filter and died. She was just soo skinny. Her tummy was flat no matter how much she ate. Also she swam kinda funny. So if it is stress that makes sense. Mamba is healthy though. and fat. not obese, just healthy female guppy fat. She's been hiding at the bottom in the plants though and I see her eyes have gone black. When she is up at the surface, her eyes turn back to normal. So, after I have just droned on and on, my question is as the title states: why do their eyes do that?