I haven't looked through all 12 pages but there are some awesome quilts pictured. I remember reading a couple of years ago about a "rule" for using yellow in quilts.
Since it is a color that really draws the eye, if it is used in only a few blocks or pieces (such as a scrappy quilt) you need to make sure that it is distributed throughout the quilt to draw the eye to the whole quilt. I don't know if I made sense here but hope it helps.