Army Regulation AR 670-1 Chapter 20-19 to be more specific on the guidelines surrounding the usage of ceremonial blue overcoats (CBO) with white bib scarf.
The Ceremonial Blue Overcoat with white scarf is worn only on formal ceremonial occasions when (a) cold temperatures demand more protection from the elements than the Army Service Uniform coat can reasonably provide, and (b) the standard black all-weather coat is not suitable for the formality or solemnity of the occasion. Shoulder straps are worn on the CBO, and the Army Service Uniform coat may not be worn under the CBO.
My guess is a scarf https://www.marlowwhite.com/old-guard-scarf
Worn with the Military Honors Overcoat and the General Officer Ceremonial Blue Overcoat
Army Regulation AR 670-1 Chapter 20-19 to be more specific on the guidelines surrounding the usage of ceremonial blue overcoats (CBO) with white bib scarf.