If you have an edible ink printer, you'll eventually run into problems of some sort with it. A common problem is having one color stop printing while all the other ones are still working.
Here's an example on the left of a sheet I just printed out that had no yellow on it. After cursing the printer for a minute, I checked the ink levels and saw that they were fine. I'd just run a printer head cleaning a couple of days ago, so I didn't want to do that again.
One thing I noticed about the cartridge when I checked it was that the sponge in it looked like it wasn't pulling the color through to the exit hole area. I'd had this happen before with other colors, and I had tried something that worked then, so I did it again. The sheet on the right in the picture was the result, printed the way that it was supposed to.
What I did was "prime the pump," so to speak. Since the sponge looked like it had dried out a little in the area where the color comes out, I took the refill ink that I have and put a few drops onto that section of the sponge. For some reason, that seemed to get the color flowing into that area again once printing started back up.
The next time this happens to you (and it isn't a matter of if, it's a matter of when) give the priming method a try. If the sponge looks like it's dry in the area that the ink exits the cartridge, just put some ink on it and see what happens. Of course, you should also go through the cleaning cycles if it's been a while, but priming the cartridge might be a simple fix.