Car leather dye is a chemical colorant that was applied to the leather during its manufacturing process. Since leather is like your own skin, the colors become a part of the leather, just as a tattoo becomes part of your skin. This type of colorant cannot be removed. However, if the leather was colored by an application of a topical paint, that can be removed, but the leather will also become damaged. Leather seats found in cars will have been made using leather dye, and not paint. So, choose your color(s) wisely, for once they are applied, they cannot be removed.
For more info, see A Guide to Car Leather Cleaning