You can customize a vehicle by adding color and textures to it.
This is done in the same way as coloring a garment or furniture. For more information, read the Tailoring section.
Note that some colors and textures require a certain level of skill to be used. If you want a color or texture over your level of expertise, there are several players who provide this service. Check out the Community Forum, or visit the in-game hotspots in order to get in touch with one.

