Extract the textures from "Main Paintjobs" folder and drop them into the YTD's, and the livery option will show in game. This means you will need to color the car using a trainer when livery's are added. The YTD might not be able to hold more than the "Main Paintjobs" so additional paintjobs from "Others" might have to replace other paintjobs by your choice. 

If you have any questions, ask me anything in the comments section using @Zievs

NOTE: Livery's made by ReNNie, all credits goes to him!!

Have fun
~Zievs