"Blackwatch" is a term commonly associated with Scottish military regiments, particularly of the 18th century. The word originated from the tartan pattern worn by the soldiers, which featured a dark shade of blue or green and black stripes. There are a few synonyms for "blackwatch" that can be used to describe similar patterns or color schemes. "Plaid" is a broad term that can encompass a range of tartan patterns, including blackwatch, while "herringbone" refers to a zigzag pattern that can have a similar look. For the color, "midnight" or "inky" can be used to describe the dark, almost black hue that characterizes the blackwatch pattern.