Koba CuffAriana Boussard Reifel koba cuff in brass. 100% Brass Yellow Brass: The high copper content in brass can cause it to darken over time. This is primarily due to a reaction to water and humidity. Some people, depending on their personal PH balance, experience a green coloring to the skin when it comes in contact with brass. This is perfectly safe and is again due to copper, think of it the Stature of Liberty Effect. If you prefer to avoid the dark