Sounds like they are using a scheme similar to CDRW disks.
i.e. changing a compound from amorphous to crystalline and back, but it changes colour at the same time.
Would be neat if they can make reuseable "multifax" paper that isn't so expensive as eink,
even a 250x rewrite limit would save a fortune in paper not to mention the environment.
The original E-ink (aka Gyricon) was supposed to work like this, and in fact it does to some extent even though the paper is nearly 4 times thicker that of a normal A4 page.
IIRC the problem was that in order to write new information it had to have a reliable contact.
Not likely when the paper is being handled a lot and getting fingerprints etc everywhere.
The nanotitanate based E-ink works better but again this has the same problem.
Maybe the solution is to use a higher temperature variant.
Essentially the oil used is solid at room temperature but becomes a liquid inside the printer.
In fact colour could be done by using 4 different oils and printing at a lower temperature on each pass, similar to the Zink printers.
Would have the advantage that the material would be archiveable.