The reason I asked so many questions is to clarify (not to be snarky ;) ). I work with animals, but I am FAR from an expert. But, guys, sometimes bile is just bile. If the cat is fed at set intervals during the day (as in, you only give him food once in the morning, take the bowl away, and then feed him once at night, taking the bowl away after that) and he vomits before even being fed, the bile is irritating his empty stomach and causing him to vomit it up. To prevent this, you can keep the food dish down all day just as long as your cat isn't the type to empty the food dish in one sitting. But don't overfeed because it leads to chubby kitties. :P
The reason I asked about age and shots and whether he's been outside is to try to eliminate feline panleukopenia (it's sometimes called "feline distemper"). It's a highly, highly contagious disease (and fatal if not caught early enough) that usually only affects young cats if they have not been fully vaccinated against panleukopenia. If you had him at three months and he hadn't had any further shots, I would be worried he hadn't been fully vaccinated against panleukopenia and then exposed to cats who carry it. And, sometimes, vets don't give a rabies shot until about 5 or 6 months and typically that's when they give the final panleukopenia shot or sometimes even afterwards. Of course, everywhere is different with that. I've seen some vets give the whole thing (including a neutering) at three months.
And the reason I asked about food (and age as well) is because it COULD be something to do with his kidneys or liver. And it could be worms, but usually (not always) they lose a lot of weight with worms.
I know it's annoying to hear over and over again, but a vet does go to eight years of college for this thing, so it'd be a very good idea to give them a call. ;) But bile is not definitely ALWAYS a bad sign.