In order to accurately answer this question, we must first understand what gunmetal is. Gunmetal, also known as red brass in the United States, is a type of bronze - an alloy consisting of copper and tin. In addition to these two metals, gunmetal often contains small amounts of zinc and lead. The exact proportions of the metals used vary depending on the desired properties of the final product.
Now that we know what gunmetal is, we can better understand its color. When freshly cut, gunmetal has a silvery appearance with a bluish tint - this is due to the high copper content. However, when exposed to air or water, gunmetal will quickly develop a reddish-brown patina. This change in color is caused by the oxidation of the copper in gunmetal; over time, the metal will continue to darken until it reaches a deep brown or black coloration.
So, in short, gunmetal metallic is typically some shade of brown - either light or dark depending on its age and exposure to the elements.