Also I want to point out that gloss is now computed by the engine. So you should use a gloss map/specular map instead of putting it into the diffuse texture.
If you want to make something that will be included in the core game, you should use gloss map. The biggest advantage is they react to the environment around them. Which means if you are in a track with a sun set, the gloss will be slightly pinkish and if you are in the middle of the desert, it will be blue.
Everything is explained here
http://supertuxkart.sourceforge.net/Tra ... d_MaterialYou can check the karts, Xue, Amanda, Adiumy who use the new system.
ALSO VERY IMPORTANT1) The kart preview is too dark this is a know bug. Please never use this to tweak the gloss map.
2) Always test the kart in a next generation track, namely Cocoa Temple & Gran Paradiso. Older tracks don't use all effects so you might tweak them in a wrong way.