@SaintFox,

With P6, and perhaps later versions, in addition to the things mentioned by MikeJ and odf, there is a setting in Render Settings > Preview > Transparency Display. The default is 90% transparent. You may need to set this to "Actual" or "Limit To 100%" to make the toecaps completely invisible in preview. Unfortunately there seems to be no way to override this user setting with a pz2 or cr2, it's purely an interface thing. In versions prior to P6 invisible materials will display as a cloud of dots, and there is nothing that can be done about it. All the above only applies to preview, and has no effect on the rendered image, which is taken care of by odf's advice.