First, please try restarting the device.

If a simple restart doesn't help, it’s a good idea to cold boot your device. To cold boot your device, hold down Home button and Power button at the same time for at least 10 seconds until the phone restarts.

If this doesn't help, the ultimate solution would be reinstalling the app. If you're willing to try reinstalling, just make sure that, before deleting, your iCloud backup is on - go to the iOS settings, find 'Recolor' and make sure it has the 'Use iCloud' on. Then, go to the settings in Recolor and check the iCloud state in the settings to make sure that iCloud is enabled. Make sure iCloud is all synced and everything is downloaded. This way you will be able to retrieve all your works when you reinstall.