Coloring books generally have a theme of sorts. It might be that they are based on a Disney movie, or it is about animals, or vehicles, or something else. When selecting books for your children, remember that they will want to express their creativity, and will have a lot of fun with any coloring book, but will be more interested in a coloring booklet with a theme that appeals to them. Choose a color book that features their favorite characters, or the item of interest in their life. For example, if your little boy just loves trains, get a Thomas the Train coloring book. If your little girl is as girly as they come, look for the Disney Princess coloring book, or possibly Strawberry Shortcake.
Determine your childs level when it comes to coloring. Some color books provide large coloring spaces making it easier for children to color the page, stay in the lines, etc. As the child gets older, their skill level for coloring increases as well, and the difficulty of the book may as well. Some coloring books come with written instructions, and other games, such as a dot to dot, or a maze. If you want to keep your child happy, and still challenge them, choose coloring or activity books in their range or level, and do not frustrate them with books that have too small of pictures, or too many spaces to color, or written instructions.
This will help them to not only recognize different colors but to also learn the names of the different colors. Developing these skills will help in later development too as your child begins to learn to read and write. He or she can then learn how to write the names of all of the different colors. You see learning is progressive and incremental - it happens in stages. Step-by-step as I have described. This is the true beauty of learning...the more that your child puts in, the more they will get out of learning. As their knowledge grows, so will their interest in a range of different subjects.