This is a tutorial where I demo a simple setup for getting paint color selection and decal selection working in your vehicle select menus. This is geared towards a racing game setup, but the same techniques will work in any game where you want to swap textures on a character or model or add decals to that model. This tutorial is in Unity 3.56 and uses some demonstration in Autodesk Maya, though the principle of "floating" decal geometry works the same in any 3d application. You can follow this tutorial and implement this system in your own games by recreating it from the video.