Disclaimer: The Blender Render engine is on it’s last official leg in Blender, as it’s likely to be removed with Blender 2.8 (the next big release of Blender within the next year or so). At that point we will likely follow suit and phase out this course and/or chapter.
That said, I haven’t used the Blender Render texture panel in a while, but as I remember, a value of -1 serves to invert the associated texture map’s influence.
Weird..I failed to include the reflection texture in the start file. It is available in the finished file. Anyhoo I just updated the source files download with the texture available in the start file.