It seems as though it would be for some sort of recognition, almost like when during WWII the Aussies infantry wore white clothe on their backs so that their officers could see how far they advanced. Maybe it was used by the Generals to see where their officers were, and for easy recognition from the troops.
And shepards we shall be
For thee, My Lord, for thee
Power hath descended forth from thy hand
That our feet may quickly carry out thy command
So we shall flow a river forth to thee
And teeming with souls shall it ever be
In nomini Patri, et Fili, Spiritus Sancti