Variegation on this cultivar is always erratic and somewhat random. Rather than a reversion, I'd suspect the lack of current variegation is more a factor of light exposure. Heavily variegated JM's will always show more distinct variegation (more pink and white) in more shade. The more sun exposure the more green will be apparent.

Spelling is actually 'Oridono-nishiki'. As stated, variegation of this one is all over the place - since you still have some pink left there is hope that you will get a lot of pink (and white) again later at some point.

Thank you both. For me, the standout feature of this tree as opposed to other variegated trees is precisely the randomness of the variegation. It even changed during the season as days got longer and temps warmer. You never knew what it would look like every spring as it leafed out or even during the season, before the foliage turned again in the fall to reds and oranges. Hopefully the variegation will return at some point as Embothrium stated.

Update: As we get deeper into spring, it is showing far more variegation, predominantly on the outside where there is new growth. The tree is very bushy and dense. So probably a light issue as to where the most variegation occurs on it.