I bought black Wilton icing in a tube about a month ago. If there is an expiration date on there I can't see it. I was wondering how long you can keep it. It was opened and it was not refrigerated. I just used a little to do a FBT, and now I have another one to do.
Taste it. Smell it. If it's not good throw it out. If it is good, use it. I'd be more worried about separation issues after a long period of time...but you can check on that too. It's primarily sugar and sugar is a preservative....plus Wilton probably packs a bunch of preservatives in there anyway. (I don't know that for sure...it's merely conjecture on my part).
I've used them for months with out any problems. I agree with smelling/tasting it.