Travis Pastrana's Red Bull sponsored 2014 Subaru Impreza WRX STI that was raced in the 2015 Red Bull Global Rallycross Championship.
The livery_00 file goes to: Steam\steamapps\common\DiRT Rally\cars\models\stx
Dirt Rally Mod manager is incredibly useful as well.
Back up original files and enjoy.
Travis Pastrana 2015 Red Bull GRC WRX STI (RX Skin) 1.0
Travis Pastrana Red Bull Global Rallycross Subaru Impreza SRT USA