Colorful Cats is a great choice for cat (and coloring) lovers. There is a good variety of scenes and styles in the 31 drawings. The illustrations range from single images to more complex full-page designs and there is a good variety in the level of detail. I enjoyed the different styles too - some are whimsical, some more realistic.
The pages are single sided and black-backed, so they are good for coloring pencils, gel pens, and even markers. The paper is medium weight and good quality for coloring. Pages are not perforated, but with a little over-working of the binding, you can pull them out without too much difficulty. The format is 8.5" x 11" so any "keepers" are easily framed.
By essentially breaking the book's spine, you can get the book to lie quite flat - a boon to coloring. (Having been taught to be delicate with book bindings as a child, I squirm a little to make recommendations like that. But alas - let's not impede the progress of our coloring!)
You can also access a PDF file of the book, if you'd like to print additional copies of the drawing on your own paper.