That is a very odd cable, appears to be no tracer marks on one of each of the colours. Is there a second green wire and a second black wire we can't see in the picture. I.E. it's an "8 pair" cable, two of each colour?
Both the blues ought to be the first pair, but it's up to whoever installed it to choose which pair they were going to use. As said, the pairs don't seem twisted, so look forward to crappy broadband speed! The order of the colour code for the pairs is...
Blue
Orange
Green
Brown
Slate (Grey, it's known as slate though)
White
Red
Black