As explained so many times already, GSX can't just use a "PaintKit" in the way you might be accustomed to, because vehicles not only are created by combining a base color and a logo but, in addition to that, what makes GSX vehicles work, is they must follow a scoring system with a set of rules, so you can't just create a new paint and expect it to work, it might be added as a proper object with a GSX-specific class, and every new operator needs to come with a complete set of vehicles.
The process for us is automated in the build process, and it's already fairly complex as it is, but editing manually for users would be just too complex, and every change will be wiped out on the next update.
And yes, your Iran Air catering will come.
