Hi again, and thanks for your additional information.
He's vomiting yellow bile because his stomach is empty. An empty stomach produces excess acid, and this causes nausea, which causes the vomiting; if he has no stomach contents to bring up, it's just the yellow foamy stuff you see.
He may have begun vomiting due to an allergy to an ingredient or ingredients in the new food, he may have ingested a non-food or toxic item, or he may have an intestinal viral or bacterial infection. It's also possible there's a problem with his liver, pancreas or kidneys, but this can only be determined through bloodwork and a hands-on exam at the vet.
If he continues to vomit frequently, I'd bring him in to an ER vet center, as this can cause dehydration. If he's drinking that's good, but he can still become dehydrated quickly and that can cause more serious health problems. If you don't have an ER vet center nearby, you can try to call vets in the Yellow Pages that list emergency hours and phone and get someone to come into the office for him. He can be given an anti-emetic to stop the nausea/vomiting and also, something to settle his stomach. In fact, if you can call your vet or an ER vet center, check to see if you can give him 1/4-1 tablet of Pepcid AC to settle his stomach for the time being.
If he seems to be breathing normally, continues to drink, and is vomiting occasionally, you can probably wait until tomorrow, to see the vet, as you plan. Monitor him throughout the night, to see if he worsens.
I hope he'll be fine, and would you please let me know how he's doing and what the vet's findings are? Thanks,