Dummies are such a challenge because it's so very, very vague just what a dummy should be, especially after you've done a little research on sub'ing manuscripts, and all of those particulars.
A dummy just needs to be a black and white (pencil, pen, charcoal, whatever) mock-up that shows how the illustrations will be composed, where the text will be, and how the layout will flow from one page to the next. Then you should include one or more "finished" samples in full-color. And of course, just like with a MS, expect everything to be edited.
It sounds like you're on the right track. I don't think the whole dummy needs to be in color. It's really more like a storyboard for the finished book.