Is there a method?

[PhillipOwens]

Is there a method available to change the colors of already existing vehicles (those in downloaded .pak files and in the game)? Regrettably, I don't have the time to learn the intricacies of Pixel Art, so I'm curious if there's a quicker approach to recoloring or beginning with a template. I apologize if my description is unclear, and I hope you can grasp what I'm trying to convey.

[Matthew]

Welcome to the International Simutrans Forum, Philip!

If you are talking about changing an existing savegame without editing any images:

• Some vehicles will use the player colours (which are chosen for each company). Go to the Players Window and if I remember correctly you click on the name of your company. But this will affect all buildings and vehicles of the same company/player.
• In Standard, there is no way to change the colours of already existing vehicles.

But you might also mean changing vehicle image files, so that you could use the differently-coloured vehicles in both existing saves and new games. Whether that is possible depends on whether the pakset is open source (read this link if you don't know that phrase) or not.

For example, pak128.britain is open source. All the pixel art is here; take some time to have a look around ('trains' and 'bus' are good places to start). You can edit it yourself as long as you abide by the licence (full  legal text is here but you might prefer this summary, which is of a slightly different version of the licence). Many of these image files were made using 3D models in Blender, so if you don't fancy pixel art, you can change the original colours in Blender instead. Those 3D models are also open source (sometimes with slightly different licences) and are here, though unfortunately a lot have been lost to the mists of time. There are tutorials for all of these things on this site.

Some of the other paksets are also open source, so you can edit them, but some are not.

I've given you a wall of information so hopefully there's something there that answers your question. Please feel free to ask more questions when you've digested that!