Yup- its the base. It scared me half to death when I saw it, but all was well. Im still figuring out this film myself, but it was nice to know that it is the film base, and not a mistake I didnt know I could make durring the processing.
The first time I developed FOMA film I flipped out, thought I did something wrong, and came running to APUG for help.
I've grown to love the pretty blue base of FOMA films though. I know it doesn't effect printing or scanning in one way or the other but its neat and it draws attention whenever I do printing at the local rental darkroom.
I got the same blue cast on 120 Arista EDU 100. If it's made in the Czech Republic, my guess is that Foma and Arista EDU are the same films? The negs print fine on VC paper.