White is the color Chaeto turns when it dies. From my experience, portions that have turned white can not revive.
While I havent proven it scientifically, I have reason to belive that the algae has purged back all the nutrients it may have absorbed when it turns clear/white. This is not a good thing.
In experimenting with 10k bulbs (granted K-value is a VERY poor indicator if the bulb has algae useful wavelegnths or not), chaeto would sorta exist, with lots of clear spots (which I belive is dead chaeto).
PAR seems to be irrelivant to algae growth. I made a setup I thought would be slick with 6.5k bulbs that put out huge amounts of light onto the algae. The algae just turned clear and died slowly, exactly the same way it dies in my tests where I keep it in the dark.
Get proper lighting.