You can use anything you like for a blackbook, but traditionally its black. scrap paper is ok, but with a book you can leaf back and learn from your previous efforts. Its too easy to lose stuff if you use scraps. if you fill a book, get a new one and put the other somewhere safe. You'll develop your own style quicker by retrospection than you will by biting from your betters. It takes a long time to understand how what you've bitten works and flows. If you actually worked something out in your book yourself you already know how it flows and can take it even further. Who knows, maybe you'll come up with something no ones seen.
i use 2 hardcover travel sketch books. 1 is my blackbook where i work on tags and throws (and try piece layouts. I know I dont have the skills, but a toys gotta dream right?) In my 2nd book i'm writing a novel. Its not for anyone else but me. Its a great way to practice your handie. when i look back at early pages i can see slow improvement in form and fluidity. As kewl as a mad wildstyle piece may be, when you do your first full page of neat flowing handie, you'll feel like you've really accomplished something. This was stressed to me time and again.
And seriously consider adding a handie book to your blackbook and practice your handwriting too. How can you write your name up for all to see when you cant write a fucking sentence legibly.