An example of the specific article of interest is the flat, light blue item worn by each individual in the below photo:
(Photo source: http://graduation.aces.illinois.edu/sites/graduation.aces.illinois.edu/themes/sitetheme/templates/images/Graduation-Large-Box-01.jpg, accessed 21 Feb 2016)
It does not appear to fit the definition of a sash or baldric or shoulder belt (these three drawn from this English.SE question), but I may be interpreting the definitions of these too strictly.
Best Answer
Graduation stole or academic stole:
Here's a photo from the same page with the graduation stole highlighted:
By Valedictorian_Joint-Chiefs-of-Staff.jpg: Chairman of the Joint Chiefs of Staffderivative work: Themightyquill - This file was derived from Valedictorian Joint-Chiefs-of-Staff.jpg:, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=20548944
[Wikipedia]
Apparently, the term graduation sash is common too:
However, a sash typically goes diagonally across the body, like what pageant queens wear (see WBT's comment below). Sticking to stole is the safest thing to do.