So, how do we think Newkirk's jumper came to be that shade of blue. As far as I know, there weren't any issue knitted jumpers at that time, let alone blue ones. The conclusion I have to come to has to be prison laundry. At some point, it was washed with Newkirk's battledress, and it 'borrowed' some of the colour.
I feel as though this was something LeBeau did to him out of pettiness during the early stages of them meeting and now Newkirk just has to live with it.