316L steel, or surgical steel as it is also called, is the material that most of our jewelry is made of. It contains about 17% chromium, 12% nickel and 2.2% molybdenum, but it is so tightly bound in the metal that less than 0.1 millionth of a gram of nickel is released per cm2 and week. It is so little that 316L passes the EU directive for products that come into close and long-term contact with the skin. The limit value is 0.5 millionths of a gram/cm2/week. "Normal" nickel allergy sufferers usually cope with the steel just fine, but if you are very sensitive or worried, you can choose titanium instead.
The colored part of the jewelry is PVD coating, it is 316L Steel covered with a thin plasma film. The thin film is very strong and does not fade. The technology has been used since the end of the 80s and is used, among other things, for implants to provide an extra hard-wearing surface.