If window tint for cars turns purple, it is not necessarily due to error on the part of the installer. In fact, the color change is related to the quality of the window tint. Cheap window tint is not made out of high quality materials. After a certain amount of time, this material starts to break down, which allows the sun's rays into it. When this happens, the suns rays start to bleach out the black color. This leads to the purple color and, in many cases, it also creates bubbles.