I have an estimated 17 hour plate that I launched a few hours ago. I am doing this with our Glow-in-the-dark PLA filament. Although I ran a long purge on the nozzle, I did not completely clean out the entire extruder -- and I just saw signs of contamination from the previously loaded blue ABS.
My guess here is that ABS dust in the drive gear is to blame. Since the print is otherwise looking pretty good, I am letting the job finish. Hopefully, the blue will be subtle enough not to be a problem. It will probably not matter at all when these items are glowing in the dark.