First off, the 3 checkmarks - tresspassing means walking inside the claim and -looking- (not looting) containers and whatever.
Theft means lifting objects and looting containers inside your claim.
Vandalism means destroying objects inside your claim.
Now, the colors... On your kinlist (Ctrl + B) you can add friends and people you know, you can then further assign colors to people, so let's say you assign me to the green color.
You can then hit the green color when configuring your personal claim, and you can decide which checkmarks to cross, for example allowing me to loot things on your claim.
You can set all of your 'purple' friends to be allowed to destroy things on your claim, and set all your 'blue' friends to be only allowed to walk around and look into containers, for example.
Edit: Ninja'd! So rude Burg
