Vomitus and fecal colors, gastric secretions
Bile is greenish. If the vomitus includes the yellow-green color of bile, it has come from the small intestine. If feces is green or brown, it generally contains bile. Brown comes from microbial changes in the bile. The green of herbivore feces is directly related to their diet.
Yellow or orange
Yellow is likely a combination of bile and normal stomach mucus. Orange stool may indicate excess bilirubin secretion, limited bile secretion, and/or incomplete fat digestion due to limited bile salts, pancreatic dysfunction or rapid transit times. Many times it just indicates dyes in the food.
Red vomitus (hematemesis) indicates a bleeding ulcer or erosion. This also means it hasn’t been digested. It could be from the oral cavity or esophagus or could be moving out of the animal before digestion can happen (eg from the stomach but without digestion).
For practical purposes lower GI bleeding is defined as bleeding that occurs in the lower GI tract and is not digested. It presents as hematochezia (bright or dark red blood in the feces). Infectious disease agents are most common causes of hematochezia.
Gray or white
White vomitus is from the stomach – no bile has been added. This generally indicates a pyloric outflow obstruction (toy, tumor).
Gray greasy feces means no bile has been secreted into the lumen to digest fats (so greasy) or add color (so gray). Pancreatic dysfunction will also lead to greasy feces.
Black or brownish black
While peptobismol and charcoal can cause black stool, brown or black vomitus or feces is generally due to digested blood. Upper GI bleeding is defined as bleeding that occurs in the stomach or small intestine, leading to digested blood in the vomit (coffee grounds) or feces (melena, black tarry feces). The most common causes of upper GI bleeding are gastric or abomasal ulceration.
Brown vomitus due to fecal contamination is very rare in animals. Bile and fat digestion create the normal brown color of dog feces.
Mucus-covered feces suggests a prolonged transit time.
What vomit colors mean – short, sweet, and similar across species!
12 things your stool says about your health – pretty easy to follow and useful for colors
Just for fun
What the color of your poop means – more rambling, less content but still good
Blood in dog stool – what to look for – scroll down for differentials