Problem with Skyboxes

I had a look at the new tutorial.base module, and I was able to add a different skybox by simply changing the path of the materialList file to the DML file I wanted. Simple and effective.

Enter Starter.fps and Racing.fps. I cannot for the life of me get that skybox I want to show up properly. When I change the materialList path to the one I want, the original skybox (clouds and what not) stays there, albeit gets dimmer. I want to get rid of those residue clouds, as they bring the undesired effect. I've tried all possible combinations of options, but to no avail.

Please help me. I want to know where (or what) did I do wrong?

Thanks.