Glad to see that it's working well for you. All the texture files for the skins should be without issue, and if there are any problems, it's likely due to changes made in the Octavia Cup mod. To my knowledge all seems to work just fine for it, though.
Apologies if you're having any issues. Try restarting your PC and then changing the track. Also update/restart java and see if that helps. If that helps fix the issue, please update the rating if you can. Thanks for the feedback, though.