Interesting! 
Are there other NATO armies, which don’t use the blue flag?
Here is what I mentioned above on a truck of the German THW, which uses the same set of flags as the Bundeswehr.
Blue flag, all convoy vehicles except the last …
… green flag, last vehicle of a convoy …
… yellow flag, vehicle has technical problems …
… red flag, towing vehicle …
… of course the THW does not use red and green flags for live fire shooting … 