It appears to be a Canon EW-100 BM neck strap that was offered as an optional accessory with many of the film EOS models, in the late 1980s to mid-2000s. The solid red EW-100 MA was also offered by Canon as an optional accessory concurrently with the EW-100 BM.
The EW-100 BM was the standard strap supplied with lower end models such as the 35mm film EOS Ti/300V introduced in 2002, the Rebel GII, a U.S. only model introduced in early 2003, the Rebel K2/3000V from late 2003, and the last EOS film camera, the Rebel T2 introduced in 2004. Other EOS film cameras, such as the EOS 1, EOS 1n, EOS 1v, EOS 3, and various EOS Elan models included a different strap in the box with the camera. None of the EOS digital cameras included the EW-100 BM in the box. The original Digital Rebel/300D introduced in 2003 supplied the EW-10DB II as the standard strap.
The color is described by Canon as Marble Blue. The strap is no longer made by Canon. References to it still exist in the accessories list on the product support pages for some older EOS film cameras and as an optional accessory on some of the earliest EOS digital models, but links to the strap are not active.
Amazon lists it in several countries but all show it as either "no longer available" or "currently unavailable." Most listings that can be found for the EW-100 BM on eBay are for used examples. Any listed as "new" are either old stock or counterfeit.
The EW-100 BM has been supplanted by several successive straps, currently the Pro Neck Strap 1, in most markets as the official replacement strap for all older and current EOS models.