Hi Keith,
I am not sure, variegated cacti are not really my thing, so I have little experience, but I wonder if it is not expressing some kind of stress response. It looks like the Gymnocalycium that you get in all the weird chlorophyl lacking colors that have to be grafted. I have a few of those with chlorophyl but they will still turn al sorts of weird colors when water/sun/temperature stressed. So it could be some kind of transplantation/transportation shock - any idea if you have it getting a lot more sunlight despite being on your windowsill?
