The term "grey mare" is typically used to describe a female horse with a dull or light grey coat. Some synonyms for this phrase are "dapple grey," which refers to a horse with gray patches over a darker base coat, "silver bay," which is a dark bay horse with silver hairs mixed in and "flea-bitten grey," a gray horse with tiny black or red spots on its coat. Other terms used to describe a grey mare might include "salt and pepper," "pewter" or "grizzle." It's important to note that the color of a horse's coat can vary greatly and it's often difficult to categorize them under one specific term.