So kinda reviving a dead thread, but I can't find any answers so I will just post what I found.
I made my first Berliner Weisse and it had a perfect color to it out of the carboy. I used White Labs Lacto in the primary. Transferred it to a keg and within a few days it had changed color to the peachy/purple color everyone's pics are showing, just like Mikeals.
It didn't taste like cardboard and while the taste wasn't exactly like a Berliner Weisse I can't say for sure that the taste was or was not compromised by this. It tasted the same until we finished the keg and we obviously drank it so it wasn't a horrible off flavor. Plus it happened almost immediately.
Cleaned out the keg yesterday and all the yeast and sediment was purple.
Here is a pic of the stuff on my finger: