Euro Truck Simulator 2 should allow for a novel way to customize truck paints without having to go the hardcore route and re-create the whole truck texture from scratch. The game will ship with a selection of proto-paintjobs - patterns encoded in RGBA channels of an image - and the player will be able to assign any color value to any of the channels. This way anybody can easily get a vast number of paintjob combinations for his truck fleet without having to use any mods, just using the built-in functions of the game.
The images below are an illustration of this approach - they are all based on the same pattern, the same proto-paintjob, with different colors chosen.