I agree that a random farmer would have BMW coolant- Perhaps there is another brand that is offering blue coolant? I have seen some water pump lubricants the same blue color, and some diesel engine cooling system additives that are also blue(stops cavitation) Maybe it is coolant from a tractor/implement manufacture? A quick google search shows that most european coolant is blue or red. which does not really help out here. I would tend to leave the coolant pure- possibly different chemical combinations effect the colors - I would probably flush and switch to prestone green, or something that is regularly available to you.
Ford, I know not the most popular here has a diesel anti-cavitation additive(I have some in my garage for my 85 ford diesel, and it tints everything blue-green, if you use to much it is blue.
Hope this helps anyways-
