I have an oldish batch of Xtol (around 10 months?) that's been stored in a mylar bladder. Just this week, it has started to pour out of the development tank as piss-yellow instead of clear though I haven't seen any reduction in development activity. The yellowness isn't just with TMY2 either, I got bright green from a batch of 4x5 Fomapan instead of blue.
I don't have any more film to develop at the moment but that will change in a week or two so I'll try a pre-wash to see if that changes anything.