I can't seem to fix it. It's a bug! We need to wait for an update I guess. Can anyone here contact the makers of the ESL/Competition title pack about what their plans are? Are they aware of this?
Edit. strangely the 2 dirt tracks in the solo campaign don't have white dirt. But when I make a new track the dirt is white. Derp.
Edit2. The forward slash in the track name has to go because MP4 sees it as a folder.
Edit3. I asked for a fix on the MP forum:
https://forum.maniaplanet.com/viewtopic.php?p=287956#p287956