https://www.europeanwatch.com/blog/rolex-gmt-master-1675-blueberry-review/

The Rolex Blueberry GMT, easily picked out of the crowd on account of its all blue bezel, is one of the most enigmatic and desired vintage Rolex models out there. Despite being such a highly collectible and valuable timepiece— it often commands a substantial premium over a standard 1675—there are still many unanswered questions about its origins and even legitimacy. There are all kinds of legends about the watch. Some claim a batch of blue bezels was saved from a factory fire by a brave worker, with all the rest getting burned up. Others say Rolex has confirmed that they never made a Blueberry GMT, while some claim the opposite. We may never know the truth, but the scholarly consensus is that rare genuine examples exist, and those examples share some generally agreed-upon traits.

First, this all blue bezel was only made for the reference 1675 Rolex GMT-Master from the 1970s. This timing lines up with Rolex’s introduction of all black bezels, so part of the thinking is that the blue bezels could have been an alternative single color bezel option that Rolex was trying out. The blue bezel has been found on Mark 2, 3, 4, and 5 dials. This specific example is a Mark 2, which you can tell by the wider “Rolex” font and logo as well as the closeness of the “LE.” Most people also agree that the blue bezel was not a standard retail configuration for the GMT, but rather it was offered to clients by Rolex Service centers. It’s also believed that the blue bezels may have been allocated specifically for military orders in the Middle East. There have been multiple co-branded United Arab Emirates GMTs that have these blueberry inserts, which helps back this theory. Additionally, there are small hallmarks like the font and an alignment notch on the back of these bezels that help when validating them...