Kriston:

DS6 likes the Singapore Math books. He prefers the textbook much better than the workbook. I think it's largely b/c the textbook is in color and the workbook isn't, but it also lets him move more quickly. I tend to take the textbook away every so often and only give him the workbook to make sure he really gets the practice and know that he's learned what he's supposed to.

I don't know why Singapore Math doesn't just do everything in color, even though it might cost a bit more. My older one had the same issue -- loved all the color placement tests and textbook; once he saw the b&w workbooks, he simply decided he'd learn math another way. Seems so silly!