A "Color by Number" app is a digital coloring book that allows users to color various pictures based on a numbered color key. Users select a picture they want to color and then fill in each section with the corresponding color according to the numbers. This type of app is often used for relaxation and creativity, as it provides a guided way to create beautiful artwork without the need for artistic skills.

Key features of a color by number app may include:

Numerous Coloring Pages: A wide variety of pictures ranging from simple to complex designs, including animals, birds, mandalas, and more.

Numbered Color Key: Each section of the picture is assigned a number that corresponds to a specific color in the app's palette.

Color Palette: A selection of colors that users can choose from to color the pages, often including a wide range of shades and hues.

Undo: The ability to undo coloring actions, allowing users to correct mistakes or experiment with different colors.

Zoom and Pan: The ability to zoom in on specific areas of the picture for easier coloring, as well as the option to move the picture around for better access.

Save and Share: The option to save completed artwork to the device's gallery and share it on social media platforms.

Overall, a coloring book app provides users of all ages with a fun and interactive way to unleash their creativity and enjoy the therapeutic benefits of coloring.