I should update the tutorial too add this sort of thing, I've been emailed a few times about it.
Anyways, in the particle settings there is a render section. In that section there is a setting labeled Material and you can set that to 1, 2, 3...etc. What that number means is that it will use the nth material for the object. For example, if you choose 2, it will use the second material in the list of materials for that object for the particles. Then you can have the other material for the ground.