https://phys.org/news/2018-07-stripes-cool-dont-zebras.html

One of several theories is that it keeps them cool in the sunshine. The black stripes get warmer than the white areas, and the theory states that this creates small vortexes when the hotter air above the dark fur meets the cooler air above the white fur. According to the theory these vortexes works as a fan to cool the body.

To test this theory, the researchers filled big metal barrels with water and covered them with skin imitations in different colours: black and white stripes, black, white, brown and grey. They then placed the barrels in the sun and later measured the temperature in each barrel. Not surprisingly, the black one was the hottest and the white one the coolest. The striped and grey barrels were similar, and in these the temperature did not go down.