Shadows are Silvers who can bend light. They can become invisible by manipulating the light around themselves. Their ability can also be extended to make others invisible. They are usually used as spies.
"Shadows are elementals, manipulators of light. Their abilities can be used to darken or brighten a room, for example, or even render themselves invisible to the human eye. Like silks, shadows are valued spies in most Silver armies and courts. Noble shadow families often elevate themselves through political scheming rather than wealth or marriage." -Victoria Aveyard "War Storm" "On Silverblooded Abilities"