Does writing icing expire?!
Answers: Yes. It's good for about a year unopened, and it gets about a month after the seal has been broken. You can tell it's going bad if the color starts to separate or if it starts to thicken.
Technically no, however, it can separate and harden in the container or take on a different color. I always plan on using my icing's within a couple of months to ensure freshness. If they become "stiff", place tube in warm water and work with fingers to soften up.
Its only sugars and color, so its unlikely to "go bad" except that it can dry up and become unusable.