As if being able to set the train color wasn't enough, as if being able to set the colors for multiple areas on the train wasn't enough, as if being able quickly apply identical liveries wasn't enough, as if having the option of multiple different presets wasn't enough, as if packing it all into one user-friendly formspec wasn't enough, on top of all that there's an instant 360° 3D preview!
Seriously though. This mod is extremely thorough, well-thought-out, and easy-to-use! From a player's perspective, the tool is simple to use and everything is laid out in a clean and orderly fashion. The Update/Save/Apply buttons are the tiniest bit demanding, you have to remember to push them in the right order before you exit the formspecs. However the temporary template save feature is very nice; it enables you to save the current livery settings and then apply them to other train cars, for customizing large trains. The 3D preview is awesome, enabling you to view what the customizations will look like on your train before actually applying them, and it can be rotated in all directions!
From a developer's perspective, it has a little bit of a learning curve (partly due to lack of detailed documentation, which is still in progress). However its overall design makes sense; once you figure it out it's easy to add more customizable areas to your registered train cars.
So I definitely recommend this mod! It offers almost limitless livery customization to Advanced Trains, and packs it all into an organized, functional, and fancy UI! Well done Marnack, I admire your work!