The following steps help solve most issues:

Go to Apple App Store -> Updates, find Recolor and make sure that you have the latest version. If the button says 'update', please tap it to instal latest update.

To restart your iOS device:
- Press and hold Home and Lock buttons simultaneously until Apple logo appears.
- iPhone 8, X and newer: Press and release volume button. Press and hold the side button until your screen turns off and on again. Release the button when Apple logo appears.

After above steps, open Recolor again and see if the issue still persists.

Check the articles under Solutions menu to see if there already is a quick fix for the issue you are experiencing.