Dogs learn a lot through their noses, including when they smell each others' rears. A lthough not the most glamorous what color is cat anal glands fluid of canine anatomy, anal sacs serve some important purposes. Anal sacs -- sometimes referred to as anal glands, even though they aren't actually glands -- are also a common source of infections in many dogs. Anal sac liquid is supposed to be dark brown or a grayish-brown color. Ideally, it's oily and fairly fluid in consistency, though some dogs naturally produce a thicker discharge. When everything's working properly, this fluid drains efficiently through short, narrow ducts and is expelled near the anus.