THis is BLUE.....There is a very specific process of controlled rust that makes this finish...IT is quite expensive to make it nice....
This is BLACK ...it's paint. It is NOT Blue...
This is a black or Parkerized slide, on an ALUMINUM frame....
This is Stainless steel, or often called "Inox"... Which is from the term "Inoxidable" which means Resistant to rust.....