Solution for having no sound on iPad:

We're sorry about the trouble. 

Apple added a "mute" option to the side switch of the iPad (In the recent iOS updates).
So now if you have no sound, your iPad probably went into "silent" mode. 

This is confusing since other apps are playing sounds, however "Sound Touch & Music Color" are using a different audio mechanism.

Since the side switch might be on "mute", please try to switch it on.

If the switch doesn't affect the sound - go to "Settings" -> "General" -> "Use side switch to:" and choose "Mute".
Now try the switch again.(see screenshot).

Now the sound should work.
Enjoy!