Sorry if this has been answered already, I quickly browsed the opening livery thread post and it's do's and don't. I did a mp race at RD yesterday and downloaded a P3 pack which had 5 or so paints in it. When I got on track the entire field was split up between those 5 paints. My question is....does the game only show the paints I've downloaded or does it show each individual users paint they are running? I found it odd that everyone was running the same pack as me.
I believe the way it works is when you download a livery pack, the custom liveries override the default liveries on your system. So custom_livery_1 will override default_1, custom_livery_2 will override default_2, and so on. So if you have the custom livery pack installed and enter a multiplayer session where someone else is using one of the default liveries, for example default_2, then you will see their car with custom_livery_2 applied from your perspective. Even if this other user has a completely different custom livery pack installed, they will be displayed from your perspective using whichever livery you have in the same slot as they're using.