How to get rotational difference to work correctly? I am following this book on animation, and I cannot understand this particular part. You are supposed to create a corrective shape key, to make the character's belt look good when the leg is posed forward in an extreme way. You can see the part of the book I'm talking about in the link (it's a legal free Google preview). 

I don't understand how to create the target bone he talks about. I go into edit mode and extrude one out of where the thigh bone comes out, but it doesn't look green like the others. In his picture they are all green, mine are too, except for the new one I create. I went ahead and created the driver anyway, and used that bone as the target bone, and the right DEF.thigh bone as the other bone for the rotational difference, but it isn't working correctly. It's like the shape key activated in the rest position too. Here's what it looks like.
Bones look green when they have bone constraints.

The video showing the problem with the driver no longer exists.
The book shows what the driver function should look like in Figure 5.59. Does the driver configuration look the same?