I had this happen to a set of screen cells a few years back. Seemed a bit darker. Then we started getting positive screens. I cultured the screens and grew yeast. The patients were sensitive to yeast. Sending the screens to another blood bank for testing showed them as negative. About a week later we received a notice from the company in the mail and new screen cells. Another time the company called us to let us know not to use a panel and sent a new one. It turned black at room temp immediately! I didn’t culture that one. And we have seen it happen to one cell in a panel. Culture if you can, as I’m sure you aren’t alone.
Our waters come in at room temp, right after collection and are set up then. If they come in on the evening shift they may sit refrigerated overnight. I'm not sure why your people transport them so cold, as it would take much longer for the cultures to grow from what viable organisms remained if they were frozen ( one article suggested up to 29 days vs a week). I'm supposing the time elapsed is long enough that they want to make sure they stay refrigerated, but not frozen?