As Google TTS was recently updated, a new feature (Number Processing) was created.Tap Speaking voice (engine, male / ...) from the top left menu of the app, then tap the Settings icon on the right side of the Preferred engine. Then turn off the Number Processing switch. Then the app won't say ': colon' anymore. Please check below 2 pictures. https://play.google.com/store/apps/developer?id=Comost..