An "app that changes hair color" is a software application that digitally modifies the color of hair in an image. One example is the "Hair Color Changer" app, which allows users to experiment with different hair colors on a photo of themselves.
These apps are becoming increasingly popular as they offer a convenient and affordable way to preview hair color changes without the commitment or expense of a salon visit. They can also be used to correct hair color mistakes or to create unique and artistic effects.