True Tone is a feature on iPhones that adjusts the color and intensity of the display to match the ambient light, making images appear more natural. True Tone is on by default and uses advanced sensors to measure the ambient light color and brightness. If you turn off True Tone, the display keeps color and intensity constant, regardless of changes in the ambient light. True Tone can be turned on or off in the Display & Brightness settings. Some display accessibility settings, including Invert Colors, Grayscale, and Increase Contrast, might turn off True Tone. True Tone is related to Night Shift, which adjusts the colors of the display to the warmer end of the spectrum and makes the display easier on your eyes.

In summary, True Tone is a feature on iPhones that adjusts the color and intensity of the display to match the ambient light, making images appear more natural. It can be turned on or off in the Display & Brightness settings and is related to Night Shift.