In December, four apps hit the top 10 on the App Store, including Sandbox Coloring, Pixel Art – Color by Number, UNICORN – Number Coloring Book, and Color by Number: Coloring Book.

For their part, Kuuhubb recently raised $20 million in funding to grow and improve Recolor, a mobile coloring book app it acquired as part of the Sumoing Oy deal. With this investment from backers ...