Hi
Recently, I have been working on some blender skripts for VDrift.
Writing a track editor skript I created a track to test the editor. A user in the vdrift forum suggested, this track would be great for supertuxkart.
I am not sure if it really fits your Visual Art Style Guidelines. But anyway, feel free to use/modify it for supertuxkart.
http://svn.vdrift.net/viewvc.cgi/trunk/models/tracks/rainbow/?root=VDrift+Art
PS: Yes, it is heavily influenced by the Rainbow Road in Mario Kart 64.