Have a look at this thread on the g503 forum:
http://g503.com/forums/viewtopic.php?f=37&t=188105
There are jerrycans with these blue lines painted on them and there is still no good explanation for them.
Does anyone here have a good suggestion? As you can see my thought are along the lines of a POM marking. IS there anything on the A list on supply depots in Normandy?
Reinier