I like ColoringBook. Not perfect, but really, really good. (Perhaps a 4.5?) There is a wide range of art to color, from abstract to goofy to complex. Some of the art should have been tested before release: when the lines dividing sections of the picture are flawed, you get adjacent sections the same color, so you may get weird results. (Hmm, blue face, or tan sky?) In other cases it just challenges my resourcefulness. The range of hues and tints is limited and uneven, especially in lighter shades. But hey, it’s a free app, and they do keep adding new art!
I got a couple of coloring books from other sources, and they have LOADS more problems with incomplete borders between sections, and areas so small that you have to tap a dozen or so times before the program realizes you want to color that area. This book is WAY easier to use.
Add-on comment, October 2021
Thanks for continuing to update your coloring book. I continue to enjoy it, and appreciate the new pages you keep adding. The new pages that I’ve done are usually problem-free. I like this feature: If you want to reuse a color, but you don’t know which pale green or whatever it was, you can place your finger on that color in any picture, and it shows you in the color family it was picked from.