Custom paints are really interesting in leagues if using the same car with the same livery for one whole championship.
Very interesting also if drivers are in team of 2 or 3 drivers using the same livery with different number of course.
Not very interesting if each driver use different cars of course ... due to the organization it needs.
The server admin and all drivers need to have your custom paint.... and you need all other drivers own custom paints.
- What the server admin needs is of course the precise name of the custom painted car folder ... in order to make this special livery name appear in the entry_list for those races
- what all drivers need is the full folder of each custom livery of all drivers in their own game.
So mostly the only good solution is ... before starting the championship, the league admin or a member of the league organization needs to ask drivers to send him the zipped folder of their custom liveries, then create and upload a full zipped pack with those liveries which all drivers will have to download and install in their game.
That's mostly how it is organized in leagues ( anyway all I knew or ran
)
EDIT:
Without custom paints ... a usual "Pickup" server only needs to specify an original skin for each entry and no driver's name and Steam Community ID in its entry_list file.
With custom paints .... this entry_list file will need the car folder names also... but the driver's name and his Steam ID for each livery.
So ...the server admin needs also to know this Steam Community ID to create his server files.