For each title I made two skins: one shiny silver with opaque stickers, and one opaque white/gray with shiny stickers:
Download (11MB)
On all skins I also applied 1x the darkening detail layer with shadows.
Btw. it happened a few times that this layer was not applied properly, instead some color or texture (like the big ManiaPlanet logo) was applied instead of the shadows

I think there is a memory leak or pointer issue somewhere.
In Canyon I also did one skin that has additional dust layer (don't know where this comes from, but it looks interesting).
And here a set of screenshots with different skins before and after driving on dirt / dusty roads:
Download (91MB)
Summary:
- the dust covers mostly opaque everything except the windows and the light glasses, working with all 3 TM² titles
- on Stadium, the side parts of the StadiuMCar are getting almost opaque from the dust, but the upper side (of the side boxes and of the car) and also the helmet are still to shiny, the dust is not opaque there