There is a Plumeria society and it has an Ask an Expert service that may be of use. There are many questions on line about Plumeria changing the color of the blooms. The President of the Plumeria society reports it happened to hers after it did not get full sunlight. Others gave theirs too much fertilizer and made the soil too acidic.
http://theplumeriasociety.org/plumeria-care/
Color change does is not normal but seems to occur .
http://homeguides.sfgate.com/care-pruning-potted-frangipani-25003.html

Congratulations on getting it to rebloom. It appears to be rather tricky or difficult and not many are successful.