Gekko is supposed to be two-tone, it is the two-tone sport of 'Kagetsu'.
As always with colours in azaleas, the purple flowers are most dominant, then the red, and then the white/pale flowers. The progression is from white to coloured. And for red colour to purple colour. And generally, there are no reversions, or you can't count on them.
So the risk is that you lose the white flowers (in fact, normally a Gekko has already lost the white flowers). Then, you worry about all coloured flowers becoming purple. So follow the Jim Trumbly guide on pruning. So if you prune for colour variation, you'd prune off the purple branches. An all purple shoot is fine. but once that shoot becomes an entire branch, that branch will have lost the colour variations (except for unlikely reversions, which seems to have happened somewhat in your tree).
And if you want to propagate, shoots near those pale flowers would be best. Those may then become 'Kagetsu' with the potential to become 'Gekko'.
There is actually a sport in between Kagetsu and Gekko, where the flowers are all white centers and the pale and white flowers are lost. Because coloured with white center is dominant, it has some stability. So this often gets named. And then once they got a two-colour version, they named that one 'Gekkko'.
Actually, Kagetsu is all-purple I believe. So you could actually get a red sport of Kagetsu, which maybe doesn't have a name.
It could also be that some environmental condition threw it off somewhat this year. And that next year, the pale flowers are gone?