Hi Jose,
I am happy to learn that you are about to start a national league in Spain. :)
And I agree that programming games like CoreWar and Robocode are a great and fun way for young people to learn about both AI and programming.
Regarding the background. Currently, the tiles can be turned off as a setting in Robocode (to black).
But the code for the blue_metal tiles is hardcoded. But this is something that could be changed in the code of course. It could be done using some property file to point at the image files and tell the size of the images etc.
... and used by the BattleView in the createGroundImage() method:
Currently, the easier way to change it is to unzip (and re-zip) the robocode-setup-1.9.x.x.jar file and replace the blue_metal_X.png with 5 other images of your choice. This would do the job. The tiles could be the same image or up to five different.
Cheers,
- Flemming N. Larsen