documentation
For a documentation of the different fields that define a vehicle type take a look at the tutorial on importing Battle Isle graphics.
When creating your own graphics the file tools/hexpics/hexfield.pcx should be used as the basis and the vehicle has to be painted in the hexagon there.
The colors 16 - 23 (red colortone) will be shifted depending on the player who owns the vehicle. For the second player these colors will be shifted to 24 - 31 and so on. The color #255 is transparent so fill the remaining hexagon with this color when finished.