I just finished watching the podcast and noticed you're looking for a chemist

Having never tried coffee staining a Polaroid, I could only guess at what is going on...
I know that coffee will add a "filter" on top of the image (light brownish amber) which will increase the overall density of the image. Since colors add-up differently, it is entirely possible the bluer image is simply the result of this optical illusion (a more baby blue color, thus containing more cyan added to a light brown containing more yellow should give a deeper blue if I got my color theory right...)
But on the other hand, coffee is acidic, something which could react with the alkaline goop left on the print surface to make some odd chemical reaction.
Coffee also being a developer, it is also entirely possible that the alkaline goop has a high enough PH to activate the development capacity of the coffee just a tad bit in order to affect the development...
I will keep on looking if I couldn't find something more "scientific" on the subject... we never know.
But anyways, it still was a cool experiment

and overall fun show (nice to see the guys in living moving colors

)
I was thinking about the protest and instantly thought Guinness World Record: most people in a single place at the same time who carry a camera...
(I'm happy as for once I didn't have to wait to get to the library to download it! Yeah!)