Gunmetal (#2A3439) is a very dark, muted blue hue. Gunmetal is a deep grey with a blue tint, borrowed from the bronze alloy used for cannons.
In RGB it is made of 42 red, 52 green and 57 blue. Its HSL hue angle is 200° with 15% saturation and 19% lightness, while its perceptual OKLCH lightness is 32% with a chroma of 0.016. For print, a starting CMYK mix is 26% cyan, 9% magenta, 0% yellow and 78% black.
As a text color on white, Gunmetal has a contrast ratio of 12.74:1, which passes WCAG AA for normal text. On black it reaches 1.65:1 and fails AA. If you use Gunmetal as a background, put white text on it. The APCA lightness contrast is Lc 0 for black text and Lc -102 for white text.
Its perceptual complement is #39302B, close to gunmetal. Colors that look most similar are taupe, charcoal, eggplant. It looks fairly similar to people with red-green color blindness (ΔE 1), so its meaning mostly survives.