Everytime I reboot my Xbox, it restores that blue defualt skin... anyway to fix that?

That was happening to me too so what i did instead of pressing A button when selecting skins i now press START and they get saved... don't know why but it works, try that!.. instead of using A use the START button.

Check out JSFX's "Skin Doesn't Stay" thread.

The button clicking advice info does not always work, certainly didn't for me. If it doesn't the solution has been posted here long ago and, so I've discovered, many times since. But nevertheless is quite difficult to find.

That thread ^ contains a link and my short description of the process. I used it succesfully myself only last night so I know it works.