The water in the bathtub turns blue.

This event can be explained as follows: firstly, there is a power failure and the lights cannot be turned on, so the surrounding environment will be very dark; Secondly, when you are texting, your eyes will focus on a small, bright and close position for a long time, which will lead to eye fatigue and blue color; Thirdly, if soaked for two hours, the oil secreted by the body will float on the water surface, forming an oil film, which will appear light blue due to the interference of light.