It ususally means your dog has acid reflex. My dog has the same thing but she will eat.
If he/she won't eat you can try to prop it's food bowl on a stand and that might help it not take in as much air and as a result should stop throwing up, or reduce it. If he/she continues to not eat, go to a doctor and he will perscribe some type of medicine to help cope.
My dog also eats grass and "pukes". Grass is known to help settle dogs' stomachs'. So take it outside and see if mother nature teaches him/her something new.
I hoped that help (:
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It is bile (stomach acid). Just like humans, they can produce too much from time to time.