What size should my book be?
Your book size is entirely up to you.
Common sizes include:
5 x 8
5.5 x 8.5
6 x 9
Keep in mind that larger dimensions result in a smaller page count. Your dimensions should reflect the theme of your book. For example, children's workbooks are better suited for larger dimensions; a general non-fiction book about business or money is better suited for more standard dimensions.
How do I format my book?
Module 4: Lesson 5 has all the information you need. As always, check the lesson description for links and additional information.
Can I /should I print my book(s) in color?
No. At least not on KDP, and not without a massive increase in retail price. We do NOT recommend printing in color because the cost to print color on KDP is high and does not lend itself to a very good profit margin. We recommend printing in Black and White ONLY (please see print cost estimator in the next question).