True Tone is a toggle-able feature, which Apple first introduced with the iPad Pro 9.7, back in 2016. Since then, it has rolled out for different iPhone models and even the latest MacBook Pros.

Basically, with True Tone on, your device will use its sensors to analyze the ambient light around you. Then, it will do minor adjustments to its display's color and whitepoint calibration, making for a more natural viewing experience.