I did some simple tests, solo with Templer at GR 25 (so mobs would only tickles me).
I blinded white, blue, yellow & purple (RG). There doesn’t seem to have any falloff (immunity). 100% I blasted shield glare (repeatedly on same mobs at least 5-6 x), 100% of the time they are blinded.
The exception is jaggunaunt (spelling?), which still showed the yellow blinded bubble on their head, but it had “immune” word flashing for 1 sec when you blind them.
Not sure in a group, if other hard CC like freeze will make mobs have blind immunity, but so far solo, using only slow from BotT, I can blind 100%.
This means (at least solo) you do not need to save blind before the holy cycle to use it.