Cat with cold just vomitted

Our one cat had a cold a few weeks ago.... now she's getting better but the other cat has what seems to be a mild cold. I really thought she was getting better today but a few minutes ago she let out a moan and then vomitted on the floor by her litter box (one large puddle, with two smaller puddles). Eyes are bright, she's loving, and right afterward she ate treats and did that little paw thing on my shoes. Anything to worry about?

... and I just noticed she has diarrhea. She made it to the box, though. I am waiting for a call-back from the on-call vet now. It's been about 30 mins since she vomitted and seems fine otherwise aside from the loose stools.

The loose stools and vomiting are not normal so it's good that you called a vet. She might have an intestinal or stomach infection but only a doctor can tell for sure.
Get a stool sample and some of the vomit if possible. Plastic yogurt containers are excellent for keeping samples. You should bring them and the cat to the vet as quickly as possible. I hope the cat is better soon.

Well the on-call vet never called me back last night. I'm assuming there was another emergency or something. Anyway, I have a call into her regular vet right now to see if he wants to see her. After she vomitted, her appetite was normal and so was her demeanor. Then the diarrhea (I followed her to her litter boxd, poor thing!).

*phew*! Vet called, I told him what happened... he said that she should be ok... just to keep a close eye on her. As long as there are no more episodes, its probably just a GI disturbance. But if her demeanor changes or the vomitting/diarrhea continues, then he wants to see her at once. She's resting comfortably on the bed now, even came out to inspect the company we had over earlier.... so I think it's safe to say all should be well.