Color Farm by Lois Ehlert is a great book for toddlers and young preschoolers. I suggest you find the board book version of this book because the pages have shape cut outs that are easily ripped if little hands grab them, the board book is sturdy! There isn't much text, just shapes and colors that together form farm animals then reveal a shape after turning the page. My son even at 3 loves this book because it's "magic" how the animals transform. The colors are bright and vivid and great for the littlest readers.
Color Dance by Ann Jonas is a great book about color mixing, and i have used it to teach the concept with kids as old as 5. In the book dancers mix their scarves together as they trail behind them. What I love about this book is that it doesn't just talk about what happens when you mix 2 colors but how you can get different shades, and that if you mix 2 parts of the same colors nothing will happen. My main complaint is that the red in the book looks pink and can really confuse kids.
The Sound Of Colors by Jimmy Liao made me weepy. It's a beautiful book abut a little girl who has lost her sight and is on a journey through subways to find colors, and dive into her own imagination. This book is long, but great for 4 year olds and older who have a keen interest in books. The imagination of this author is amazing and your kids will enjoy it but I suspect you will love it !
I Love Colors by Margaret Miller is a great book for babies. The text simply announces the color of the specific item the baby on each page is wearing or holding. What makes this book stand out for me is that the photos of the babies are almost life size and their expressions will engage your baby as well.