I think there are so many misconceptions around LEDs even after several years of use and a more mainstream acceptance. You could happily grow corals under nothing but white LEDs. The coral would get enough light for photosynthesis and grow but the colours would not look pleasing to our eyes. You could also probably grow corals under nothing but blue LEDs but, again, the colour would likely not be what we want for our own enjoyment.
All the other colours of LEDs being added to fixtures; green, red, violet; are not necessary for growth or coral health but are useful to fine tune the "look" of the corals for us.
As for the topic of this thread, bleaching does indicate too much light. Blue is high in PAR in the spectrum that corals utilize so turning them down or raising your fixture will help. And you need to give the corals time to acclimate to the new light intensity. They won't change overnight.
IME, it's better to start LEDs higher or at lower power and have your corals start to brown a bit, then turn them up or lower them than it is to shock them with too much light and bleach and potentially kill them.
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