According to Canva: Gray is a mixture of black and white. It is timeless and versatile, making it a great partner to a wide variety of colors. It is associated with cloudy days and, as a result, is not the cheeriest color. Gray, however, is often used in interior design to create a contemporary and sophisticated feel. Like most other neutrals, gray can be combined with almost any other color in the visible spectrum.
Gray looks BEAUTIFUL on a chestnut, and also works well with Black and lighter grey (white) coats. It would get lost on a dapple gray. But can also look very sophisticated on any of the brown tones. It also works well with other color accents like turquoise, pink and green.