Beginning in 1954, the GMT-Master II’s bezel was made of Plexiglas, with the color and white indexes printed on the back. From 1959 to 2007, Rolex made its bezels from aluminum and painted them in color by anodizing. Since then, color has followed on tracks made of zirconia ceramic. A single-color bezel was standard, as a two-color track seemed technically impossible. But Rolex persisted in its research and found a solution for the first Batman in 2013. It developed and patented a process for monochromatic bezels in which metallic salts are added to one-half of the bezel before it is heat-treated in a kiln. The final color is created by sintering the watch in a kiln at 1600 degrees Celsius for over 24 hours. 
The second problem was achieving the desired red color for the blue-red Pepsi bezel, as no mineral-based pigments could produce a rich red color. After years of research, Rolex began to rely on an alumina-based ceramic with the addition of chromium oxide, magnesium oxide and rare earth oxides to produce the red portion of the ceramic bezel. To obtain the blue color, half of the bezel was again saturated with a metallic salt solution before being sintered.
The bezels of Batman and Pepsi are based on different ceramic substances, namely zirconium oxide and aluminum oxide, which explains why the blue color of the two bezels looks so different. On our replica watch, the blue color looks much brighter than on the new Pepsi model. However, incident light plays a major role in our perception of color, and as usual, there are subtle differences between the Pepsi bezels.
Both materials used to form the track condense and shrink during the sintering process and must be machined to exact dimensions using diamond tools. To ensure that the numerals remain perfectly readable, the entire ring is coated with platinum using a PVD process and then carefully polished to leave the precious metal in the recessed dots and numerals. Rolex patents both processes. In addition to being scratch-resistant, ceramic bezels have the added advantage of being UV-resistant and will not fade.